be quiet vs belt up

be quiet and belt up both are verbs.

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

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

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

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