ON'SET, noun [on and set.] 1. A rushing or setting upon; a violent attack; assault; a storming; appropriately, the assault of an army or body of troops upon an enemy or a fort. The shout of battle now began and rushing sound of onset 2. An attack of any kind; as the impetuous onset of grief. ON'SET, verb transitive To assault; to begin. [Not used.]
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI