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).
Words nearby keep a civil tongue in one's head
keene,
keene's cement,
keener,
keening,
keep,
keep a civil tongue in one's head,
keep a low profile,
keep a sharp lookout,
keep a stiff upper lip,
keep a straight face,
keep a weather eye out