close up vs shut up

close up is not an adjective while shut up is an adjective.

Word	Noun	Adjective	Verb	Adverb
close up	No	No	Yes	Yes
shut up	No	Yes	Yes	No

As verbs, close up and shut up are synonyms defined as:

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

close up (adjective)	shut up (adjective)
	closely confined

close up (verb)	shut up (verb)
refuse to talk or stop talking; fall silent	cause to be quiet or not talk
block passage through	refuse to talk or stop talking; fall silent
unite or bring into contact or bring together the edges of	place in a place where something cannot be removed or someone cannot escape
cease to operate or cause to cease operating

close up (adverb)	shut up (adverb)
very close