Definition of "onset"

Heralds, from off our towers, we might beholdFrom first to last, the onset and retireOf both your armies

c. 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, [Act II, scene i]

Who on that day the word of onset gave.

1800, William Wordsworth, Six thousand Veterans

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

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

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

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

And will with deeds requite thy gentleness:And, for an onset, Titus, to advanceThy 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, [Act I, scene i]