noun,pluralbig·mouths[big-mouthz, -mouths] /ˈbɪgˌmaʊðz, -ˌmaʊθs/ for 1; (especially collectively) big·mouth, (especially referring to two or more kinds or species) big·mouthsfor 2.
a loud, talkative person, especially one who lacks discretion.
any of several fishes having an unusually large mouth.