Noun

(en noun)

A rushing or setting upon; an attack; an assault; a storming; especially, the assault of an army.

* (rfdate) (William Shakespeare),

The onset and retire / Of both your armies.

* (rfdate) (William Wordsworth),

Who on that day the word of onset gave.

(medicine) The initial phase of a disease or condition, in which symptoms first become apparent.

(phonology) The initial portion of a syllable, preceding the syllable nucleus.

(acoustics) The beginning of a musical note or other sound, in which the amplitude rises from zero to an initial peak.

(obsolete) A setting about; a beginning.

* (rfdate) (Francis Bacon),

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

(obsolete) Anything set on, or added, as an ornament or as a useful appendage.

* {{quote-magazine, date=2013-06-29, volume=407, issue=8842, page=28, magazine=(The Economist)

, title= High and wet , passage=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.}}

(Shakespeare)

(Johnson)