hostile fire vs firing

hostile fire and firing both are nouns.

Word	Noun	Adjective	Verb	Adverb
hostile fire	Yes	No	No	No
firing	Yes	No	No	No

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

Other hypernyms of hostile fire include fire.

hostile fire (noun)	firing (noun)
fire that injures or kills an enemy	the act of setting something on fire
	the termination of someone's employment (leaving them free to depart)
	the act of discharging a gun
	the act of firing weapons or artillery at an enemy