keep/hold/play your cards close to your chest
play your cards close to your chestmainly BRITISH or
play your cards close to the vestAMERICAN
If you play your cards close to your chest, you do not tell anyone about your plans or thoughts. Williams is playing his cards close to his chest, especially in terms of his driver line-up for next season. He plays his cards very close to the vest, leaving some attorneys with whom he's worked to describe him as secretive and manipulative. Note: You can also say that someone keeps their cards close to their chest or keeps their cards close to the vest. The Prime Minister was said yesterday to be keeping his cards close to his chest after an informal discussion at cabinet on Thursday. Note: Other nouns are sometimes used instead of cards. Taylor kept his thoughts close to his chest, saying only: `I'm not prepared to comment.' I have no inside information — Dave's playing this one close to his chest. The military's playing this whole operation pretty close to the vest — they generally don't like to talk about future operations. Note: This is a reference to card-players holding their cards close to their chest so that nobody else can see them.
keep (or play) your cards close to your chest (or vest)be extremely secretive and cautious about something. informal
The previous two idioms both refer to a hand of cards in a card game. If you hold all the cards you have a winning hand, while card players who hold their cards close to their bodies ensure that no opponent can look at them.