Repay

wiktionary

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From Old French repaier(“to pay back”) (compare French repayer(“to pay again”)).

etymonline

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repay (v.)

mid-15c., repaien, "pay back, refund," from Old French repaier, repaiier, "pay back, give in return," from re- "back" (see re-) + payer "to pay" (see pay (v.)).

The sense of "give (one thing) in return for (another)" is from 1550s; that of "make return, retribution, or requital for," in a good or bad sense is by 1590s. Related: Repaid; repaying; repayable.