Etymology From on- + set. Compare Old English onsettan (“to impose; oppress, bear down”). For semantic parallels for the meaning to assault, compare cognate Russian насе́сть pf (naséstʹ), наседа́ть impf (nasedátʹ).
1
Medicine, Sciences The initial phase of a disease or condition, in which symptoms first become apparent.
the onset of schizophrenia
In mild cases of hypergonadism prior to puberty, the onset of physical and mood changes may not be abnormally early or significant enough to cause any psychological or long-term physical complications.2018 June 25, James Roland, “What is Hypergonadism?”, in Healthline, archived from the original on 25 Apr 2025:
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Widely credited as an early pioneer of the modern railway, Shooter died peacefully of his own choosing in Switzerland on December 13, having bravely lived with the onset of motor neurone disease in the final years of his life.2022 December 28, Paul Stephen, “Network News: Adrian Shooter CBE: rail industry mourns "a great man"”, in RAIL, number 973, page 6:
2
Human sciences, Linguistics, Phonology, Sciences The initial portion of a syllable, preceding the syllable nucleus.
The only regular sources for Sardinian *θ are Lat. ci̯ and ti̯, which are absent from Latin onsets. This means that the substantial number of words starting in *θ, discussed in § 3 – 7, cannot regularly continue a Latin form.2025, Cid Swanenvleugel, The Pre-Roman Elements of the Sardinian Lexicon, page 390:
3
The beginning of a musical note or other sound, in which the amplitude rises from zero to an initial peak.
4
A setting about; a beginning.
the onset of puberty
There is surely no greater wisdom than well to time the beginnings and onsets of things.1625, Francis [Bacon], “Of Delays”, in The Essayes […], 3rd edition, London: […] Iohn Haviland for Hanna Barret, →OCLC:
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Floods in northern India, mostly in the small state of Uttarakhand, have wrought disaster on an enormous scale. The early, intense onset of the monsoon on June 14th swelled rivers, washing away roads, bridges, hotels and even whole villages. Rock-filled torrents smashed vehicles and homes, burying victims under rubble and sludge.2013 June 29, “High and wet”, in The Economist, volume 407, number 8842, page 28:
5
Obsolete Anything added, such as an ornament or as a useful appendage.
And will with deeds requite thy gentleness: And, for an onset, Titus, to advance Thy name and honourable family, Lavinia will I make my empress.c. 1588–1593 (date written), William Shakespeare, “The Lamentable Tragedy of Titus Andronicus”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act I, scene i]:
6
Archaic An attack; an assault especially of an army.
Heralds, from off our towers, we might behold From first to last, the onset and retire Of both your armiesc. 1596 (date written), William Shakespeare, “The Life and Death of King Iohn”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act II, scene i]:
Who on that day the word of onset gave.1800, William Wordsworth, Six thousand Veterans:
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And Peter's tired army cheered, and the newcomers roared, and the enemy squealed and gibbered till the wood re-echoed with the din of that onset.1950, C. S. Lewis, The Lion, the Witch and the Wardrobe:
Etymology From on- + set. Compare Old English onsettan (“to impose; oppress, bear down”). For semantic parallels for the meaning to assault, compare cognate Russian насе́сть pf (naséstʹ), наседа́ть impf (nasedátʹ).