clam up


clam up
clam up
to say nothing. (Closing one's mouth in the way that a clam closes up.) •

The minute they got him in for questioning, he clammed up.

You'll clam up if you know what's good for you.

* * *
{v.}, {slang} To refuse to say anything more; stop talking. * /The suspect clammed up, and the police could get no more information out of him./

Dictionary of American idioms. 2013.