a beginning or start

the onset of winter.

an assault or attack

an onset of the enemy.

Phonetics . the segment of a syllable preceding the nucleus, as the gr in great. Compare coda ( def. 5 ) , core ( def. 14 ) .

noun

conclusion , end , ending , finish

noun

access , aggression , assailment , assault , birth , charge , commencement , dawn , dawning , encounter , inception , incipience , kickoff * , offense , offensive , onfall , onrush , onslaught , opening , origin , outbreak , outset , outstart , rush , seizure , start , attempt , strike , beginning , genesis , nascence , nascency , spring , attack , dash , push , raid