back up vs close up

back up and close up both are verbs.

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

As verbs, close up is a hypernym of back up; that is, close up is a word with a broader meaning than back up:

Other hypernyms of back up include block, impede, jam, obstruct, obturate, occlude.

back up (verb)	close up (verb)
establish as valid or genuine	refuse to talk or stop talking; fall silent
become or cause to become obstructed	block passage through
make a copy of (a computer file) especially for storage in another place as a security copy	unite or bring into contact or bring together the edges of
move backwards from a certain position	cease to operate or cause to cease operating
give moral or psychological support, aid, or courage to

back up (adverb)	close up (adverb)
	very close