dummy up vs keep mum

dummy up and keep mum both are verbs.

Word	Noun	Adjective	Verb	Adverb
dummy up	No	No	Yes	No
keep mum	No	No	Yes	No

As verbs, dummy up and keep mum are synonyms defined as:

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

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