stoolpigeon vs blabber

stoolpigeon and blabber both are nouns.

Word	Noun	Adjective	Verb	Adverb
stoolpigeon	Yes	No	No	No
blabber	Yes	No	Yes	No

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

stoolpigeon: 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 stoolpigeon include betrayer, informer, rat, squealer.

stoolpigeon (noun)	blabber (noun)
someone acting as an informer or decoy for the police	one who reveals confidential information to the police or other authority

stoolpigeon (verb)	blabber (verb)
	speak (about unimportant matters) rapidly and incessantly