c. 1300, rewarden, "to grant, bestow;" early 14c. "to give as prize or compensation," from Anglo-French and Old North French rewarder "to regard, reward" (Old French regarder) "take notice of, regard, watch over." This is from re-, here perhaps an intensive prefix (see re-), + warder "look, heed, watch," from Frankish or some other Germanic language, from Proto-Germanic *wardon "to guard" (from PIE root *wer- (3) "perceive, watch out for").
Originally any form of requital, good or bad, for service or evil-doing. A doublet of regard (v.), reward was used 14c.-15c. in the senses now given to that word: "look at; care about; consider." Related: Rewarded; rewarding.
<a href="https://www.etymonline.com/word/rewarding">Etymology of rewarding by etymonline</a>
Harper, D. (n.d.). Etymology of rewarding. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/rewarding