stool pigeon vs blabber

stool pigeon and blabber both are nouns.

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

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

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

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

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

stool pigeon (verb)	blabber (verb)
	speak (about unimportant matters) rapidly and incessantly