onslaught vs onrush

onslaught and onrush both are nouns.

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

As nouns, onslaught and onrush are synonyms defined as:

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

Other synonyms of onslaught include attack, onset.

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