Perpendicular to the vertical; parallel to the plane of the horizon; level, flat.
horizontal lines
I also claim the combination of the separator shaft with the shoe, and with the pitman, for the purpose of imparting to it a recriprocating horizontal movement, and a vibratory movement on its axis at the same time,...1847, editorial staff, “Winnowing Machines”, in Scientific American, series 1, Volume 3, Issue 9, page 68:
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Power is derived from a British United Traction Limited "A"-type 150-h.p. six-cylinder horizontal diesel engine; this drives through a fluid flywheel, and thence through a free wheel unit to a four-speed epicyclic gearbox.1958 April 23, “Diesel Railbus for British Railways”, in Railway Magazine, page 275:
[…] a pair of pauldrons with the light horizontal bar which in later years developed into the high neckguard of the sixteenth century; numbers of gauntlets, visors of helmets, and other pieces, the handling of which is a sheer joy […]1976, Apollo: A Journal of the Arts:
As when the Sun new ris'n / Looks through the Horizontal misty Air1667, John Milton, “Book I”, in Paradise Lost. […], London: […] [Samuel Simmons], and are to be sold by Peter Parker […]; [a]nd by Robert Boulter […]; [a]nd Matthias Walker, […], →OCLC; republished as Paradise Lost in Ten Books: […], London: Basil Montagu Pickering […], 1873, →OCLC, lines 594-595:
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Beverages, Food, Lifestyle, Oenology, Wine Involving wines of the same vintages but from different wineries.
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Entertainment, Lifestyle, MusicOf an interval Having the two notes sound successively.
Comparing a man who inspires you intellectually and makes you laugh with a guy who fulfils all your horizontal desires means you’re not comparing like with like.2020 February 2, Mariella Frostrup, “One is a great guy; the other is good in bed. So who do I choose?”, in The Guardian:
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Biology, Natural sciences Being or relating to the transmission of organisms between biotic and/or abiotic members of an ecosystem that are not in a parent-progeny relationship.
Infectious agents may spread by horizontal transmission.