1. {v. phr.}, {slang} To say something of great importance or meaning; say more by a sentence than the words usually mean. - Usually in past tense. * /Tom said a mouthful when he guessed that company was coming to visit. A dozen people came./ 2. {v. phr.}, {informal} To vent one's honest opinion, even in anger. * /He sure said a mouthful when he told his boss what was wrong with our business./ Contrast: GET AN EARFUL.
SAY A MOUTHFUL
Meaning of SAY A MOUTHFUL in English
Slang English vocab. Английский сленговый словарь. 2012