harassing fire vs firing

harassing fire and firing both are nouns.

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

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

harassing fire: fire designed to disturb the rest of enemy troops and to curtail movement and to lower enemy morale
firing: the act of firing weapons or artillery at an enemy

Other hypernyms of harassing fire include fire.

harassing fire (noun)	firing (noun)
fire designed to disturb the rest of enemy troops and to curtail movement and to lower enemy morale	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