pay back vs repay

pay back and repay both are verbs.

Word	Noun	Adjective	Verb	Adverb
pay back	No	No	Yes	No
repay	No	No	Yes	No

As verbs, pay back and repay are synonyms defined as:

pay back and repay: act or give recompense in recognition of someone's behavior or actions

Other synonyms of pay back include reward.

pay back (verb)	repay (verb)
take vengeance on or get even	answer back
act or give recompense in recognition of someone's behavior or actions	pay back
	make repayment for or return something
	act or give recompense in recognition of someone's behavior or actions