Idioms of Secrecy

Is a secret safe with you? Here are some English idioms about telling a secret and keeping a secret.

Telling secrets

to leak = to let a secret out: "Somebody has leaked the diplomatic cables." (If something leaks, it lets out water.)

whistle blower = someone who blows the whistle on an organisation tells the wider world about bad / illegal practices: "Whistle blowers aren't always protected by the law."
spill the beans = to tell a secret: "Josie spilled the beans on her relationship with her boss."
let the cat out of the bag = let a secret out: "Don't let the cat out of the bag! I want his present to be a secret."
crack under pressure = tell something because you've been under pressure to: "The criminal cracked under pressure of his interrogation and confessed to robbery."
take the lid off something = reveal a secret: "He's taken the lid off what really happens in animal testing labs."
Some gossip idioms:
dish the dirt = tell the public about an ex: "Is she going to dish the dirt on her footballer husband?"
kiss and tell = a story told by an ex: "In the latest kiss and tell, we hear all about a Hollywood actor."
be a blabbermouth = tell everything (blab = slang for talk): "She's such a blabbermouth. I can't believe she told you!"

Keeping a secret

keep mum = keep quiet: "Can you keep mum? I've got something to tell you."
stay schtum = stay silent: "If you can stay schtum, I want to say something to you…"
my lips are sealed = I won't say a word: "You can trust me. My lips are sealed."
keep a poker face = not give away anything: "If you can keep a poker face, people will tell you secrets."
take your secret to the grave with you = never reveal a secret: "Unfortunately, he took his secret to the grave with him. We'll never know the truth."
keep something under wraps = keep something secret: "They kept their plans under wraps."