From Longman Dictionary of Contemporary Englishdown in the mouthdown in the mouthinformalSAD/UNHAPPY unhappy Tim’s looking very down in the mouth. → mouth
Examples from the Corpus
down in the mouth• He was no longer down in the mouth.• I have, as you know, been slightly down in the mouth.• Why do you look so down in the mouth today?• Peter saw him the other night, Max, said he looked very down in the mouth. 