supporting fire vs firing

supporting fire and firing both are nouns.

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

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

supporting fire: fire delivered by supporting units to protect or assist a unit in combat
firing: the act of firing weapons or artillery at an enemy

Other hypernyms of supporting fire include fire.

supporting fire (noun)	firing (noun)
fire delivered by supporting units to protect or assist a unit in combat	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