belt up vs button up

belt up and button up both are verbs.

Word	Noun	Adjective	Verb	Adverb
belt up	No	No	Yes	No
button up	No	No	Yes	No

As verbs, belt up and button up are synonyms defined as:

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

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