push back vs repel

push back is a noun but repel is not a noun.

Word	Noun	Adjective	Verb	Adverb
push back	Yes	No	Yes	No
repel	No	No	Yes	No

As verbs, push back and repel are synonyms defined as:

Other synonyms of push back include beat back, drive, force back, repulse.

push back (noun)	repel (noun)
the act of forcing the enemy to withdraw

push back (verb)	repel (verb)
cause to move back by force or influence	reject outright and bluntly
	force or drive back
	cause to move back by force or influence
	be repellent to; cause aversion in
	fill with distaste