niff vs reek

niff and reek both are nouns.

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

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

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

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

niff (verb)	reek (verb)
	be wet with sweat or blood, as of one's face
	smell badly and offensively
	have an element suggestive (of something)
	give off smoke, fumes, warm vapour, steam, etc.