keep mum vs be quiet

keep mum and be quiet both are verbs.

Word	Noun	Adjective	Verb	Adverb
keep mum	No	No	Yes	No
be quiet	No	No	Yes	No

As verbs, keep mum and be quiet are synonyms defined as:

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

keep mum (verb)	be quiet (verb)
refuse to talk or stop talking; fall silent	refuse to talk or stop talking; fall silent