stool pigeon vs betrayer

stool pigeon and betrayer both are nouns.

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

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

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

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

stool pigeon (noun)	betrayer (noun)
a dummy pigeon used to decoy others	a person who says one thing and does another
someone acting as an informer or decoy for the police	one who reveals confidential information to the police or other authority