firing vs onrush

firing and onrush both are nouns.

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

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

Other hypernyms of firing include attack, onset, onslaught.

firing (noun)	onrush (noun)
the act of setting something on fire	(military) an offensive against an enemy (using weapons)
the termination of someone's employment (leaving them free to depart)	a forceful forward rush or flow
the act of discharging a gun
the act of firing weapons or artillery at an enemy