firing vs ignition

firing and ignition both are nouns.

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

As nouns, firing and ignition are synonyms defined as:

Other synonyms of firing include inflammation, kindling, lighting.

firing (noun)	ignition (noun)
the act of setting something on fire	the act of setting something on fire
the termination of someone's employment (leaving them free to depart)	the mechanism that ignites the fuel in an internal-combustion engine
the act of discharging a gun	the process of initiating combustion or catching fire
the act of firing weapons or artillery at an enemy