tight lips

hang tight

To wait, without attempting to address a challenging, alarming, or dangerous situation, until a later point in time.

keep one's lips sealed

To keep quiet; to keep a secret; to not tell.

loosen someone's lips

To cause one to speak more freely; to cause one to discuss a subject that would not usually be discussed.

one's lips are sealed

One will not tell anyone else; one is keeping a secret.

read lips

To lipread.

read someone's lips

To pay close attention (often imperative).

sit tight

To wait patiently; to take no action; to remain quiet or relatively motionless.

tight ship

A well-organized and highly disciplined organization.