stench vs odor

stench and odor both are nouns.

Word	Noun	Adjective	Verb	Adverb
stench	Yes	No	No	No
odor	Yes	No	No	No

As nouns, odor is a hypernym of stench; that is, odor is a word with a broader meaning than stench:

stench: a distinctive odor that is offensively unpleasant
odor: the sensation that results when olfactory receptors in the nose are stimulated by particular chemicals in gaseous form

Other hypernyms of stench include odour, olfactory perception, olfactory sensation, smell.

stench (noun)	odor (noun)
a distinctive odor that is offensively unpleasant	any property detected by the olfactory system
	the sensation that results when olfactory receptors in the nose are stimulated by particular chemicals in gaseous form