Noah Webster
Onset
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.]