clam up

== English == === Etymology === By analogy with a clam closing itself. Compare clamshell (“mouth”), clam (“mouth”). === Pronunciation === === Verb === clam up (third-person singular simple present clams up, present participle clamming up, simple past and past participle clammed up) (intransitive, informal) To become silent; to stop talking. Synonyms: shut up, shut up like a clam; see also Thesaurus:be quiet (ambitransitive) To make or become clammy. ==== Antonyms ==== talk ==== Translations ====