13c., raunsoun, "sum paid for the release of a prisoner or captured man," also "redemption from damnation," from Old French ranson (Modern French rançon), earlier raenson "ransom, redemption," from Latin redemptionem (nominative redemptio) "a redeeming," from redimere "to redeem, buy back," from red- "back" (see re-) + emere "to take, buy, gain, procure" (from PIE root *em- "to take, distribute"). A doublet of redemption. A faded word somewhat revived by Scott early 19c. Spelling with -m appears by late 14c., but the reason for it is unclear (compare seldom, random).
"buy back, redeem by paying or giving in return that which is demanded," early 14c., raunsounen, from ransom (n.). Related: Ransomed; ransoming.