onrush vs onslaught

onrush and onslaught both are nouns.

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

As nouns, onrush and onslaught are synonyms defined as:

onrush and onslaught: (military) an offensive against an enemy (using weapons)

Other synonyms of onrush include attack, onset.

onrush (noun)	onslaught (noun)
(military) an offensive against an enemy (using weapons)	(military) an offensive against an enemy (using weapons)
a forceful forward rush or flow	the rapid and continuous delivery of linguistic communication (spoken or written)
	a sudden and severe onset of trouble