be tight-lipped

be tight-lipped

1. Literally, to have one's lips pressed together, as in anger. I knew my girlfriend was angry as soon as I saw that she was tight-lipped and glaring at me.
2. To be unwilling to talk openly or share details about someone or something. I still don't know anything about Maria's new boyfriend because she's so tight-lipped about him. Don't worry, we can trust my sister to be tight-lipped—she won't tell anyone about our engagement until we do.
Farlex Dictionary of Idioms.
See also:
  • tight-lipped
  • smack (one's) lips
  • lick/smack your lips
  • (one's) lips turn blue
  • glare
  • glare at
  • glare at (someone or something)
  • glaring
  • girlfriend
  • read my lips