On"set` (?), n. [On + set.] 1. A rushing or setting upon; an attack; an assault; a storming; especially, the assault of an army. Milton.

The onset and retire
Of both your armies.

Who on that day the word of onset gave.

2. A setting about; a beginning. [Obs.] Shak.

There is surely no greater wisdom than well to time the beginnings and onsets of things.

3. Anything set on, or added, as an ornament or as a useful appendage. [Obs.] Johnson.

On"set`, v. t. 1. To assault; to set upon. [Obs.]

2. To set about; to begin. [Obs.] Carew.