Idioms and Phrases with keep a civil tongue in one's head
keep a civil tongue in one's head
Speak politely, as in The teacher won't allow swearing; she says we must keep a civil tongue in our heads. This expression uses tongue in the sense of “a manner of speaking,” a usage dating from the 1400s. An early cautionary version was “Keep a good tongue in your head, lest it hurt your teeth” (1595).