bombardment vs onset

bombardment and onset both are nouns.

Word	Noun	Adjective	Verb	Adverb
bombardment	Yes	No	No	No
onset	Yes	No	No	No

As nouns, onset is a hypernym of bombardment; that is, onset is a word with a broader meaning than bombardment:

Other hypernyms of bombardment include attack, onrush, onslaught.

bombardment (noun)	onset (noun)
the heavy fire of artillery to saturate an area rather than hit a specific target	(military) an offensive against an enemy (using weapons)
an attack by dropping bombs	the beginning or early stages
the act (or an instance) of subjecting a body or substance to the impact of high-energy particles (as electrons or alpha rays)
the rapid and continuous delivery of linguistic communication (spoken or written)