button one's lip

Verb

button one's lip (third-person singular simple present buttons one's lip, present participle buttoning one's lip, simple past and past participle buttoned one's lip)

1. (idiomatic) To remain silent, especially in order to keep a secret or to avoid saying something inappropriate.
   • "Yes," put in Solomon. "I've been tipped off to this guy Mars, and you'd better tell him to button up his lip and not start anything."1910, Jim Nasium, "The Baseball League on the Styx," The Sunday Press (Pittsburgh), 15 May, p. 2 (retrieved 19 July 2010)
   • "We advised John not to talk, to button his lip, but he talked anyway."1971 October 13, Ted Blackman, “Green as team player too”, in Montreal Gazette, retrieved 19 Jul 2010, page 13

   Synonyms:

   bite one's lip, zip one's lip