coup de main vs onslaught

coup de main and onslaught both are nouns.

Word	Noun	Adjective	Verb	Adverb
coup de main	Yes	No	No	No
onslaught	Yes	No	No	No

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

Other hypernyms of coup de main include attack, onrush, onset.

coup de main (noun)	onslaught (noun)
an attack without warning	(military) an offensive against an enemy (using weapons)
	the rapid and continuous delivery of linguistic communication (spoken or written)
	a sudden and severe onset of trouble