Definition from Wiktionary, the free dictionary
onset (plural onsets)
- A rushing or setting upon; an attack; an assault; a storming; especially, the assault of an army.
- (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.
- (obsolete) Anything set on, or added, as an ornament or as a useful appendage.
- the start (of something)
2013 June 29, “High and wet”, The Economist, volume 407, number 8842, page 28:
- 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.
rushing or setting upon
medicine: initial phase of a disease or condition
phonology: initial portion of a syllable