clam up vs be quiet

clam up and be quiet both are verbs.

Word	Noun	Adjective	Verb	Adverb
clam up	No	No	Yes	No
be quiet	No	No	Yes	No

As verbs, clam up and be quiet are synonyms defined as:

Other synonyms of clam up include belt up, button up, close up, dummy up, keep mum, shut up.

clam up (verb)	be quiet (verb)
refuse to talk or stop talking; fall silent	refuse to talk or stop talking; fall silent