rankle vs nark

rankle is not a noun while nark is a noun.

Word	Noun	Adjective	Verb	Adverb
rankle	No	No	Yes	No
nark	Yes	No	Yes	No

As verbs, nark is a hypernym of rankle; that is, nark is a word with a broader meaning than rankle:

Other hypernyms of rankle include annoy, bother, chafe, devil, get at, get to, gravel, irritate, nettle, rag, rile, vex.

rankle (noun)	nark (noun)
	an informer or spy working for the police
	a lawman concerned with narcotics violations

rankle (verb)	nark (verb)
gnaw into; make resentful or angry	inform or spy (for the police)
	cause annoyance in; disturb, especially by minor irritations