reimburse vs refund

reimburse is not a noun while refund is a noun.

Word	Noun	Adjective	Verb	Adverb
reimburse	No	No	Yes	No
refund	Yes	No	Yes	No

As verbs, refund is a hypernym of reimburse; that is, refund is a word with a broader meaning than reimburse:

Other hypernyms of reimburse include give back, repay, return.

reimburse (noun)	refund (noun)
	the act of returning money received previously
	money returned to a payer

reimburse (verb)	refund (verb)
pay back for some expense incurred	pay back
reimburse or compensate (someone), as for a loss