dummy up vs belt up

dummy up and belt up both are verbs.

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

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

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

dummy up (verb)	belt up (verb)
refuse to talk or stop talking; fall silent	refuse to talk or stop talking; fall silent
make a dummy of