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. Shak.
Who on that day the word of onset gave. Wordsworth.
2. A setting about; a beginning. Shak.
There is surely no greater wisdom than well to time the beginnings and onsets of things. Bacon.
3. Anything set on, or added, as an ornament or as a useful appendage. Johnson.