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Phrase(s): A still tongue makes a wise head.
Prov. If you are wise, you do not talk very much.; You should only speak when you have judged that it is appropriate to do so. • Don’t chatter about whatever comes to your mind. A still tongue makes a wise head. • Kathy really offended Mr. Parker by talking so much about his ex-wife. She needs to learn that a still tongue makes a wise head.
McGrawhill's American Idioms And Phrasal Verbs