back up vs electronic computer

back up is not a noun while electronic computer is a noun.

Word	Noun	Adjective	Verb	Adverb
back up	No	No	Yes	No
electronic computer	Yes	No	No	No

back up (noun)	electronic computer (noun)
	a machine for performing calculations automatically

back up (verb)	electronic computer (verb)
establish as valid or genuine
become or cause to become obstructed
make a copy of (a computer file) especially for storage in another place as a security copy
move backwards from a certain position
give moral or psychological support, aid, or courage to