revert vs fall back

revert and fall back both are verbs.

Word	Noun	Adjective	Verb	Adverb
revert	No	No	Yes	No
fall back	No	No	Yes	No

As verbs, fall back is a hyponym of revert; that is, fall back is a word with a more specific, narrower meaning than revert:

Other hyponyms of revert include lapse, recidivate, regress, relapse, retrogress, resile, go back, recover, recuperate.

revert (verb)	fall back (verb)
go back to a previous state	go back to bad behavior
undergo reversion, as in a mutation	retreat
	hang (back) or fall (behind) in movement, progress, development, etc.
	fall backwards and down
	move back and away from
	have recourse to