congest vs back up

congest and back up both are verbs.

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

As verbs, congest and back up are synonyms defined as:

Other synonyms of congest include choke, choke off, clog, clog up, crap up, foul.

congest (verb)	back up (verb)
become or cause to become obstructed	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