An Onset

1. (archaic) An attack; an assault especially of an army. Synonym: storming
2. (medicine) The initial phase of a disease or condition, in which symptoms first become apparent.
3. (phonology) The initial portion of a syllable, preceding the syllable nucleus. Synonym: anlaut Antonym: coda
4. (acoustics) The beginning of a musical note or other sound, in which the amplitude rises from zero to an initial peak.
5. A setting about; a beginning. Synonyms: start, beginning
6. (obsolete) Anything added, such as an ornament or as a useful appendage.