smelly vs foul-smelling

smelly and foul-smelling both are adjectives.

Word	Noun	Adjective	Verb	Adverb
smelly	No	Yes	No	No
foul-smelling	No	Yes	No	No

As adjectives, smelly and foul-smelling are synonyms defined as:

Other synonyms of smelly include fetid, foetid, foul, funky, ill-scented, noisome, stinking.

smelly (adjective)	foul-smelling (adjective)
offensively malodorous	offensively malodorous