"to give back, restore," early 15c. (earlier "to pour back," late 14c.), from Old French refunder "restore" and directly from Latin refundere "give back, restore, return," literally "pour back, flow back," from re- "back" (see re-) + fundere "to pour" (from nasalized form of PIE root *gheu- "to pour"). Specifically of money from 1550s. Related: Refunded; refunding.