blabbermouth vs gossip

blabbermouth and gossip both are nouns.

Word	Noun	Adjective	Verb	Adverb
blabbermouth	Yes	No	No	No
gossip	Yes	No	Yes	No

As nouns, gossip is a hypernym of blabbermouth; that is, gossip is a word with a broader meaning than blabbermouth:

blabbermouth: someone who gossips indiscreetly
gossip: a person given to gossiping and divulging personal information about others

Other hypernyms of blabbermouth include gossiper, gossipmonger, newsmonger, rumormonger, rumourmonger.

blabbermouth (noun)	gossip (noun)
someone who gossips indiscreetly	light informal conversation for social occasions
	a report (often malicious) about the behavior of other people
	a person given to gossiping and divulging personal information about others

blabbermouth (verb)	gossip (verb)
	wag one's tongue; speak about others and reveal secrets or intimacies
	talk socially without exchanging too much information