onset Definition

1. An attack; an assault.

Thesaurus: assault, rush, attack, encounter, onslaught.
2. A beginning, especially of something unpleasant.

Thesaurus: commencement, onslaught, outbreak, start.
3a. phonetics.
The movement of the speech organs in preparation for or at the beginning of the articulation of a sound;
3b. phonetics.
The consonant or group of consonants at the beginning of a syllable.