keep a civil tongue in one's head

Idioms  

1. 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).

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Example Sentences

I let him go on as he pleased; then I got up abruptly, I took him by the arm, and I said to him: 'M. Panckoucke, in whatever place it may be, in the street, in church, in a bad house, and to whomsoever it may be, it is always right to keep a civil tongue in one's head.

From Project Gutenberg

Bullets are much easier to put up with and keep a civil tongue in one's head.

From Project Gutenberg