odour vs foulness

odour and foulness both are nouns.

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

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

odour (noun)	foulness (noun)
any property detected by the olfactory system	the attribute of having a strong offensive smell
the sensation that results when olfactory receptors in the nose are stimulated by particular chemicals in gaseous form	(of weather) the badness of the weather
	a state characterized by foul or disgusting dirt and refuse
	disgusting wickedness and immorality