stool pigeon vs squealer

stool pigeon and squealer both are nouns.

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

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

stool pigeon: someone acting as an informer or decoy for the police
squealer: one who reveals confidential information to the police or other authority

Other hypernyms of stool pigeon include betrayer, blabber, informer, rat.

stool pigeon (noun)	squealer (noun)
a dummy pigeon used to decoy others	domestic swine
someone acting as an informer or decoy for the police	one who reveals confidential information to the police or other authority