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.
rushing or setting upon
medicine: initial phase of a disease or condition
phonology: initial portion of a syllable