last gasp vs ending

last gasp and ending both are nouns.

Word	Noun	Adjective	Verb	Adverb
last gasp	Yes	No	No	No
ending	Yes	No	No	No

As nouns, ending is a hypernym of last gasp; that is, ending is a word with a broader meaning than last gasp:

Other hypernyms of last gasp include end.

last gasp (noun)	ending (noun)
the point of death or exhaustion or completion	the act of ending something
	the end of a word (a suffix or inflectional ending or final morpheme)
	the last section of a communication
	event whose occurrence ends something
	the point in time at which something ends