bombing vs onslaught

bombing and onslaught both are nouns.

Word	Noun	Adjective	Verb	Adverb
bombing	Yes	No	No	No
onslaught	Yes	No	No	No

As nouns, onslaught is a hypernym of bombing; that is, onslaught is a word with a broader meaning than bombing:

Other hypernyms of bombing include attack, onrush, onset.

bombing (noun)	onslaught (noun)
an attack by dropping bombs	(military) an offensive against an enemy (using weapons)
the use of bombs for sabotage; a tactic frequently used by terrorists	the rapid and continuous delivery of linguistic communication (spoken or written)
	a sudden and severe onset of trouble