Etymology From Middle English flat, a borrowing from Old Norse flatr (compare Norwegian and Swedish flat, Danish flad), from Proto-Germanic *flataz, from Proto-Indo-European *pleth₂- (“flat”); akin to Saterland Frisian flot (“smooth”), German Flöz (“a geological layer”), Ancient Greek πλατύς (platús), Latvian plats, Sanskrit प्रथस् (prathas, “extension”). Doublet of plat and pleyt. The noun is from Middle English flat (“level piece of ground, flat edge of a weapon”), from the adjective. The algebraic sense was coined by Serre in a 1956 paper, originally as French plat.
Smooth; having no protrusions, indentations or other surface irregularities, or relatively so.
The surface of the mirror must be completely flat.
The carpet isn't properly flat in that corner.
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She has quite a flat face.
The face which emerged was not reassuring. It was blunt and grey, the nose springing thick and flat from high on the frontal bone of the forehead, whilst his eyes were narrow slits of dark in a tight bandage of tissue. […].1963, Margery Allingham, chapter 17, in The China Governess: A Mystery, London: Chatto & Windus, →OCLC:
This early slowdown is one piece of a broader evolutionary trend known as gracilization, the tendency for modern humans to become more delicate in form. Our bones are thinner, our muscles smaller, and our faces flatter than those of earlier hominins.2025 November 27, Tibi Puiu, “This Is Why Modern Human Faces Look So Different From Neanderthals”, in ZME Science, archived from the original on 23 Feb 2026:
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Slang Having small or invisible breasts and/or buttocks.
Near-synonym: flat-chested
That girl is completely flat on both sides.
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Without variation in level, quantity, value, tone etc.
The exchange rate has been flat for several weeks.
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At a consistently depressed level; consistently lacklustre.
Sales have been flat all year, and we've barely broken even.
Human sciences, Linguistics, Phonetics, Phonology, SciencesOf a vowel Not diphthongal; without variation in height or backness.
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Of colours Without variation in tone or hue (uniform), and dull (not glossy).
The walls were painted a flat gray.
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Figuratively Lacking liveliness or action; depressed; uninteresting; dull and boring.
The party was a bit flat.
The market is flat today as most traders are on holiday.
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The dialogue in your screenplay is flat — you need to make it more exciting.
February 16, 1833, Samuel Taylor Coleridge, Table Talk A large part of the work is, to me, very flat.
How weary, stale, flat, and unprofitable / Seem to me all the uses of this world.c. 1599–1602 (date written), William Shakespeare, “The Tragedie of Hamlet, Prince of Denmarke”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act I, scene ii]:
Entertainment, Lifestyle, Music Of a note or voice, lower in pitch than it should be.
Your A string is flat.
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Absolute; downright; peremptory.
His claim was in flat contradiction to experimental results.
I'm not going to the party and that's flat.
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Wag[ner]. Vilaine, call me Maiſter Wagner, and let thy left eye be diametarily fixt vpon my right heele, with quaſi veſtigias nostras inſistere [as if to follow in our footsteps]. / Clo[wn]: God forgiue me, he ſpeakes Dutch fuſtian: / well, Ile folow him, Ile ſerue him, thats flat.1589–1592 (date written), Ch[ristopher] Marl[owe], The Tragicall History of D. Faustus. […], London: […] V[alentine] S[immes] for Thomas Bushell, published 1604, →OCLC, signature [B4], recto:
SECOND WATCH. Marry, that he had received a thousand ducats of Don John for accusing the Lady Hero wrongfully. DOGBERRY. Flat burglary as ever was committed1598–1599 (first performance), William Shakespeare, “Much Adoe about Nothing”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act IV, scene ii]:
A great Tobacco taker too, thats flat.1602, John Marston, Antonio and Mellida, Malone Society Reprint, 1921, Act I, lines 324-326, He is made like a tilting staffe; and lookes For all the world like an ore-rosted pigge
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Deflated, especially because of a puncture.
Of a tire or other inflated object
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Of a carbonated drink With all or most of its carbon dioxide having come out of solution so that the drink no longer fizzes or contains any bubbles.
Human sciences, Linguistics, Phonetics, Phonology, SciencesDated, Of a consonant Sonant; vocal, as distinguished from a sharp (non-sonant) consonant.
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Grammar, Human sciences, Linguistics, Sciences Not having an inflectional ending or sign, such as a noun used as an adjective, or an adjective as an adverb, without the addition of a formative suffix; or an infinitive without the sign "to".
Many flat adverbs, as in 'run fast', 'buy cheap', etc. are from Old English.
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Golf, Hobbies, Lifestyle, SportsOf a golf club Having a head at a very obtuse angle to the shaft.
We either burns the old brooms, or, if we can, we sells ’em for a ha’penny to some other boy, if he’s flat enough to buy ’em.1851, Henry Mayhew, London Labour and the London Poor, published 1861:
Etymology From Middle English flat, a borrowing from Old Norse flatr (compare Norwegian and Swedish flat, Danish flad), from Proto-Germanic *flataz, from Proto-Indo-European *pleth₂- (“flat”); akin to Saterland Frisian flot (“smooth”), German Flöz (“a geological layer”), Ancient Greek πλατύς (platús), Latvian plats, Sanskrit प्रथस् (prathas, “extension”). Doublet of plat and pleyt. The noun is from Middle English flat (“level piece of ground, flat edge of a weapon”), from the adjective. The algebraic sense was coined by Serre in a 1956 paper, originally as French plat.
I asked him if he wanted to marry me and he turned me down flat.
"You'll understand this flat, I won't be fooled about by you any longer."1950, Norman Lindsay, Dust or Polish?, Sydney: Angus and Robertson, page 63:
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Of accurately measured timings Exactly, precisely.
In the mile race, Smith's time was 3:58.56, and Brown's was four minutes flat.
Dan Patch clocked a scorching 1:55.5 flat.1996, Jon Byrell, Lairs, Urgers and Coat-Tuggers, Sydney: Ironbark, page 186:
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I play doctor for five minutes flat Before I cut my heart open and let the air out1997, “Scissors”, performed by Slipknot:
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With units of time Used to emphasize the smallness of the measurement.
Distance; etc; distance; etc
He can run a mile in four minutes flat.
Found my coat and grabbed my hat / Made the bus in seconds flat1967, Lennon–McCartney, “A Day in the Life”, in Sgt. Pepper's Lonely Hearts Club Band:
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Of a sentence Without parole.
The recent case in Dallas where two gay males were killed by an 18 yr old straight kid is a perfect example of what gays in this state face. The kid got 30 yrs (he'll do 3 or 4 yrs and be paroled) yet I must do 12 years flat for a robbery in which no one was hurt.1989 February 5, Mary Shallhorn, “No Unity Among The Sisters”, in Gay Community News, volume 16, number 29, page 5:
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Completely.
I am flat broke this month.
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Directly; flatly.
Sin is flat opposite to the Almighty.[1633], George Herbert, edited by [Nicholas Ferrar], The Temple. Sacred Poems, and Private Ejaculations, Cambridge, Cambridgeshire: […] Thomas Buck and Roger Daniel; and are to be sold by Francis Green, […], →OCLC:
Etymology From Middle English flat, a borrowing from Old Norse flatr (compare Norwegian and Swedish flat, Danish flad), from Proto-Germanic *flataz, from Proto-Indo-European *pleth₂- (“flat”); akin to Saterland Frisian flot (“smooth”), German Flöz (“a geological layer”), Ancient Greek πλατύς (platús), Latvian plats, Sanskrit प्रथस् (prathas, “extension”). Doublet of plat and pleyt. The noun is from Middle English flat (“level piece of ground, flat edge of a weapon”), from the adjective. The algebraic sense was coined by Serre in a 1956 paper, originally as French plat.
An area of level ground (sometimes covered with shallow or tidal water).
The hovercraft skimmed across the open flats.
the eastern end of the salt flat; mud flat, tidal flat, flood flat
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Envy is as the sunbeams that beat hotter upon a bank, or steep rising ground, than upon a flat.1625, Francis [Bacon], “Of Envy”, in The Essayes […], 3rd edition, London: […] Iohn Haviland for Hanna Barret, →OCLC:
My hopes wa'n't disappointed. I never saw clams thicker than they was along them inshore flats. I filled my dreener in no time, and then it come to me that 'twouldn't be a bad idee to get a lot more, take 'em with me to Wellmouth, and peddle 'em out. Clams was fairly scarce over that side of the bay and ought to fetch a fair price.1913, Joseph C[rosby] Lincoln, chapter III, in Mr. Pratt’s Patients, New York, N.Y.; London: D[aniel] Appleton and Company, →OCLC:
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In the phrase 'the flat' Level ground in general.
I can run on the flat but not up hills.
The going will be easier once we're through these mountains and onto the flat.
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"Indeed it's troubling you too much, Sir!" the maid exclaimed. "She can walk very well on the flat."1889, Lewis Carroll, Sylvie and Bruno:
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Hobbies, Horse racing, Horseracing, Horses, Lifestyle, Pets, Racing, SportsSometimes, With 'the' or attributively, With capital Level horse-racing ground, as contrasted with courses incorporating jumps, or the racing done on such ground.
This horse will do better over the flat.
flat racing, the flat season
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In light of Horse Racing Ireland's Covid-19 contingency plan announcement, that whenever racing resumes the Flat will be given priority, Elliott has decided to keep a number of talented jumpers on the go during the summer, with a view towards a dual-purpose campaign.2020, Brian Sheerin, Racing Post, "Gordon Elliott maps out summer Flat campaigns for talented jumpers" (article) https://web.archive.org/web/20211102070751/https://www.racingpost.com/news/gordon-elliott-maps-out-summer-flat-campaigns-for-talented-jumpers/431475
2021 (retrieved), racing365.com, "Flat Racing Explained" https://racing365.com/flat-racing-explained/ In British horse racing, the classics are a series of horse races run over the flat (i.e. without jumps).
As forecast, Joe suspected nothing as he pottered round the flat in the sunshine, absorbed in the task of picking winners.1963, George Blaikie, Scandals of Australia's Strange Past, Adelaide: Rigby Limited, page 117:
Entertainment, Lifestyle, Music A note played one chromatic semitone lower than a natural, denoted by the symbol ♭ placed after the letter representing the note (e.g., B♭) or in front of the note symbol (e.g. ♭♪).
The next one surrendered his bike, only for that, too, to give him a second flat as he started the descent.2012 July 15, Richard Williams, Tour de France 2012: Carpet tacks cannot force Bradley Wiggins off track, Guardian Unlimited:
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In plural A type of ladies' shoe with a very low heel.
She liked to walk in her flats more than in her high heels.
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In plural A type of flat-soled running shoe without spikes.
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A thin, broad brush used in oil and watercolour painting.
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The most prominent flat part of something.
The outboard bales in each tier should be placed on their edges so that their flats will be presented to the sweat battens. This precaution is necessary to lessen the damage in case of chafage. If the bales chafe or become wet on their flats, only one or two layers will be damaged.2024, Robert J. Meurn, Marine Cargo Operations:
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The flat side of a blade, as opposed to the sharp edge.
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The palm of the hand, with the adjacent part of the fingers.
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A wide, shallow container or pallet.
a flat of strawberries
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US, Abbreviation, Ellipsis Ellipsis of flat water (“nonfizzy drinking water”).
Waiter: Would you like sparkling or flat? Guest: Flat, thank you.
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A large mail piece measuring at least 8 1/2 by 11 inches, such as catalogs, magazines, and unfolded paper enclosed in large envelopes.
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Rail transport, Railways, TransportUS A railroad car without a roof, and whose body is a platform without sides; a platform car or flatcar.
For example, when trailers containing new automobiles were first piggybacked two areas of potential damage became evident: (1) diesel locomotive exhaust left a film of oil on the new autos; and (2) auto windshields could be scarred or cracked by the metal-tipped "tell-tales" which warn men atop trains of oncoming bridges or tunnels. Accordingly, automobiles aboard piggyback flats are usually coupled into the train 15 or more cars behind the locomotive; and telltales have been raised.1960 November, David Morgan, “"Piggyback"—U.S. success story”, in Trains Illustrated, page 684:
The tender roared along vibrating vigorously; braking had resulted in "flats" on most of its tyres.1951 October, R. S. McNaught, “Lines of Approach”, in Railway Magazine, page 706:
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A flat-bottomed boat, without keel, and of small draught.
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Geometry, Mathematics, Sciences A subset of n-dimensional space that is congruent to a Euclidean space of lower dimension.
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A straw hat, broad-brimmed and low-crowned.
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A flat sheet for use on a bed.
You might think that Americans buy roughly the same number of fitted sheets as flats. Or, considering the market for electric blankets, duvets, and other covers, that consumers buy even more bottom sheets, simply forgoing the tops.1986, New York Magazine, volume 19, number 49, page 20:
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Media, Publishing A flat, glossy children's book with few pages.
This same publisher notes pricing is a crucial factor in the mass market field of $1, $1.95 and $2.95 "flats."1970, The Publishers Weekly, volume 197, page 85:
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A platform on a wheel, upon which emblematic designs etc. are carried in processions.
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Business, Mining A horizontal vein or ore deposit auxiliary to a main vein; also, any horizontal portion of a vein not elsewhere horizontal.
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Engineering, Natural sciences, Physical sciences, Technical A rectangular wooden structure covered with masonite, lauan, or muslin, often produced in standard modules, that is used to build wall surfaces on stage. Flats can be painted and outfitted with doors and/or windows to depict a building or other part of a scene, and are a hard-surfaced alternative to a backcloth or backdrop.
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Biology, Entomology, Natural sciences Any of various hesperiid butterflies that spread their wings open when they land.
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Historical An early kind of toy soldier having a flat design.
Among the many US museums hosting flats, we may mention the Toy Soldier Museum in the Pocono Mountains, supervised by the historian, collector and dealer J. Hillestad.2019, Luigi Toiati, The History of Toy Soldiers, page 78:
[…] if you cannot make a speech, Because you are a flat, Go very quietly and drop A button in the hat!1836, Oliver Wendell Holmes Sr., The Music-Grinders:
"He fancies he can play at billiards," said he. "I won two hundred of him at the Cocoa-Tree. HE play, the young flat! […]"1847 January – 1848 July, William Makepeace Thackeray, chapter 14, in Vanity Fair […], London: Bradbury and Evans […], published 1848, →OCLC:
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“But,” said I, “you said the other day, that you liked the fair thing.” “That was by way of gammon,” said the landlord; “just, do you see, as a Parliament cove might say speechifying from a barrel to a set of flats, whom he means to sell. Come, what do you think of the plan?”1851, George Borrow, Lavengro; the Scholar—the Gypsy—the Priest. […], volume (please specify |volume=I to III), London: John Murray […], →OCLC:
"She can indeed walk very well on the flat," I said. "And I think I was the Flat."1889, Lewis Carroll, Sylvie and Bruno:
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Abbreviation, Ellipsis Ellipsis of flat ride (“spinning amusement ride”).
"When sampling the aperture of a telescope, using auto-collimating flats (ACFs) is more economical"2013 April 1, Spechler et al., “Advanced Dispersed Fringe Sensing Algorithm for Coarse Phasing Segmented Mirror Telescopes”, in NASA Tech Briefs, retrieved 27 Dec 2021:
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Gambling, GamesSlang A cheater's die with the edges shaved to make certain rolls more likely.
He would slip in his six-ace flats, shaved dice that were made to bring up sevens. He'd throw them just long enough to get well, and then replace them with legitimate cubes.2005, Fred Cicetti, Local Angles: The Big News in Small Towns, page 78:
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British Columbia, Canadian Prairies A 24-case of beer.
Etymology From Middle English flat, a borrowing from Old Norse flatr (compare Norwegian and Swedish flat, Danish flad), from Proto-Germanic *flataz, from Proto-Indo-European *pleth₂- (“flat”); akin to Saterland Frisian flot (“smooth”), German Flöz (“a geological layer”), Ancient Greek πλατύς (platús), Latvian plats, Sanskrit प्रथस् (prathas, “extension”). Doublet of plat and pleyt. The noun is from Middle English flat (“level piece of ground, flat edge of a weapon”), from the adjective. The algebraic sense was coined by Serre in a 1956 paper, originally as French plat.
And thus thoſe Forts vvhich vvere erected to defend the Crovvne, firſt offended the King, ſome fevv vvhereof as he recouered, he flatted to the ground, and vviſhed the other no higher vvalls; ſtill ſvvearing by Gods Birth (his vſuall Oath) hee vvould not ſlightly bee vnſeated of his Crovvne, and vvondring vvhat ſhould mooue them, vvho had ſo readilie aduanced him, ſo ſpeedily to vnſtate him.1611, Iohn Speed [i.e., John Speed], “Stephen, the Two and Fortieth Monarch of the English-men: His Raigne, Acts, and Issue”, in The History of Great Britaine under the Conquests of yͤ Romans, Saxons, Danes and Normans. […], London: […] William Hall and John Beale, for John Sudbury and George Humble, […], →OCLC, book IX ([Englands Monarchs] […]), paragraph 13, page 447, column 2:
The pods, which seldom contain less than thirty nuts of the size of a flatted olive, grow upon the stem and principal branches.1764, James Granger, The Sugar-Cane: a Poem. In Four Books. With Notes., M.D., Book 1, page 44, note to verse 605:
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Dated To render dull, insipid, or spiritless; to depress.
Passions are allayed, appetites are flatted.a. 1678 (date written), Isaac Barrow, “(please specify the chapter name or sermon number)”, in The Works of Dr. Isaac Barrow. […], volume (please specify |volume=I to VII), London: A[braham] J[ohn] Valpy, […], published 1830–1831, →OCLC:
Etymology From an alteration (due to Scots flatt (“a level part of a structure”)) of Scots flet, flett (“inner part of a house”), from Middle English flet (“dwelling”), from Old English flet, flett (“ground floor, dwelling”), from Proto-West Germanic *flati, from Proto-Germanic *flatją (“floor”), from Proto-Germanic *flataz (“flat”), from Proto-Indo-European *pleth₂- (“flat”). Akin to Old Frisian flet, flette (“dwelling, house”). More at flet, flat₁.
The excellence of French flats is so well known in America, that the owner will often refer to his property as "first class French flats."1905, Sydney Perks, Residential flats of all classes, including artisans' dwellings: a practical treatise on their planning and arrangement, together with chapters on their history, financial matters, etc.,with numerous illustrations, page 204:
A kiss may be grand but it won’t pay the rental on your humble flat or help you at the automat.1953 January 1, “Diamonds Are a Girl’s Best Friend”, in My Heart Belongs to Daddy, performed by Marilyn Monroe:
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[NICELY]When you meet a gent paying all kinds of rent for a flat that could flatten the Taj Mahal. [BOTH]Call it sad, call it funny but it’s better than even money that the guy’s only doing it for some doll.1955 November 3, “Guys and Dolls”, in Guys and Dolls (Original Broadway Cast Recording), performed by Stubby Kaye (as Nicely Nicely Johnson) and Johnny Silver (as Benny Southstreet):
Fifteen percent of this group said that they were not satisfied with the public housing estates and their HDB^([Singapore Housing & Development Board]) flats (see Tables 11 and 12 respectively).1983, Tai Ching Ling, “Relocation and Population Planning: A Study of the Implications of Public Housing and Family Planning in Singapore”, in Wilfredo F. Arce, Gabriel C. Alvarez, editors, Population Change in Southeast Asia, page 184:
The Greater London Council formed the Estmanco company to manage a block of 60 council-owned flats. The council entered into an agreement with the company to sell off the flats to owner-occupiers.2002, MIchael Ottley, Briefcase on Company Law, page 76:
When the Dolphin Square's flats were first offered to the public in 1936, the South Block was still under construction, and the North Block was a building site.2014, Terry Gourvish, Dolphin Square: The History of a Unique Building, page 75:
Etymology From Middle English flatten, from Old French flatir (“to knock or strike down, dash”), from Frankish *flattjan (“to move the palm of the hand”), from Proto-Germanic *flatjaną (“to make flat, flatten”).