stool pigeon vs decoy

stool pigeon and decoy both are nouns.

Word	Noun	Adjective	Verb	Adverb
stool pigeon	Yes	No	No	No
decoy	Yes	No	Yes	No

As nouns, decoy is a hypernym of stool pigeon; that is, decoy is a word with a broader meaning than stool pigeon:

stool pigeon: a dummy pigeon used to decoy others
decoy: something used to lure fish or other animals into danger so they can be trapped or killed

Other hypernyms of stool pigeon include bait, lure.

stool pigeon (noun)	decoy (noun)
a dummy pigeon used to decoy others	something used to lure fish or other animals into danger so they can be trapped or killed
someone acting as an informer or decoy for the police	a beguiler who leads someone into danger (usually as part of a plot)

stool pigeon (verb)	decoy (verb)
	lure or entrap with or as if with a decoy