get under one's skin vs nark

get under one's skin is not a noun while nark is a noun.

Word	Noun	Adjective	Verb	Adverb
get under one's skin	No	No	Yes	No
nark	Yes	No	Yes	No

As verbs, nark is a hypernym of get under one's skin; that is, nark is a word with a broader meaning than get under one's skin:

Other hypernyms of get under one's skin include annoy, bother, chafe, devil, get at, get to, gravel, irritate, nettle, rag, rile, vex.

get under one's skin (noun)	nark (noun)
	an informer or spy working for the police
	a lawman concerned with narcotics violations

get under one's skin (verb)	nark (verb)
irritate	inform or spy (for the police)
	cause annoyance in; disturb, especially by minor irritations