fall back vs employ

fall back is not a noun while employ is a noun.

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

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

fall back: have recourse to
employ: put into service; make work or employ for a particular purpose or for its inherent or natural purpose

Other hypernyms of fall back include apply, use, utilise, utilize.

fall back (noun)	employ (noun)
	the state of being employed or having a job

fall back (verb)	employ (verb)
go back to bad behavior	put into service; make work or employ for a particular purpose or for its inherent or natural purpose
retreat	engage or hire for work
hang (back) or fall (behind) in movement, progress, development, etc.
fall backwards and down
move back and away from
have recourse to