Question

Clam Up to refuse to talk; to become silent

Accepted Answer

When the boss asked who had left the copy machine on all night, Caitlin clammed up. An imaginative writer once thought that a person's lips were like the two halves of a clamshell. When it wants to, a clam can shut its shell tightly. That's what gave that writer the idea to write "clam up" to mean "to shut your lips, and keep information to yourself." Other similar idioms are "button up," "button your lip," (see page 24), and "zip your lips."

Idiom	Clam Up
Example	When the boss asked who had left the copy machine on all night, Caitlin clammed up.
Meaning	to refuse to talk; to become silent
Origin	An imaginative writer once thought that a person's lips were like the two halves of a clamshell. When it wants to, a clam can shut its shell tightly. That's what gave that writer the idea to write "clam up" to mean "to shut your lips, and keep information to yourself." Other similar idioms are "button up," "button your lip," (see page 24), and "zip your lips."

Clam Writer Shut Button Boss Asked Left Copy