be quiet vs clam up

be quiet and clam up both are verbs.

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

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

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

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