odour vs foetor

odour and foetor both are nouns.

Word	Noun	Adjective	Verb	Adverb
odour	Yes	No	No	No
foetor	Yes	No	No	No

As nouns, foetor is a hyponym of odour; that is, foetor is a word with a more specific, narrower meaning than odour:

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

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