blabbermouth

ˈblabəmaʊθ

noun

a person who talks excessively or indiscreetly.

talker,chatterer,jabberer,babbler,prattler,blatherer,prater,tittle-tattler,tattler,gossip,gossiper,gossipmonger,conversationalist,blatherskite,chatterbox,windbag,gasbag,gabber,big mouth,loudmouth,natterer