coup de main vs onrush

coup de main and onrush both are nouns.

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

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

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

coup de main (noun)	onrush (noun)
an attack without warning	(military) an offensive against an enemy (using weapons)
	a forceful forward rush or flow