niff vs stink

niff and stink both are nouns.

Word	Noun	Adjective	Verb	Adverb
niff	Yes	No	No	No
stink	Yes	No	Yes	No

As nouns, stink is a hypernym of niff; that is, stink is a word with a broader meaning than niff:

Other hypernyms of niff include fetor, foetor, malodor, malodour, mephitis, reek, stench.

niff (noun)	stink (noun)
an unpleasant smell	a distinctive odor that is offensively unpleasant

niff (verb)	stink (verb)
	smell badly and offensively
	be extremely bad in quality or in one's performance