imperfection vs failing

imperfection and failing both are nouns.

Word	Noun	Adjective	Verb	Adverb
imperfection	Yes	No	No	No
failing	Yes	Yes	No	No

As nouns, failing is a hyponym of imperfection; that is, failing is a word with a more specific, narrower meaning than imperfection:

Other hyponyms of imperfection include weakness, flaw, defect, defect, fault, flaw, wart, defectiveness, faultiness, nonoptimality.

imperfection (noun)	failing (noun)
the state or an instance of being imperfect	failure to reach a minimum required performance
	a flaw or weak point

imperfection (adjective)	failing (adjective)
	below acceptable in performance