babblemouth

noun2

1. •
   (informal, disapproving) One who babbles.

   • I WAS WONDERING WHEN YOU WOULD PAUSE FOR BREATH… …SO I MIGHT TRY TO GET A WORD IN EDGEWISE. / I GUESS SOMETIMES I DO TURN INTO A BABBLEMOUTH--SORRY. — 1988
2. •
   (informal, rare) One who reveals or gives away information.