Is it ensure, insure, or assure?
late 14c., "piece of land enclosed for breeding beasts and fowls," from Anglo-French and Old North French warenne, Old French garenna "game park," possibly from Gaulish *varenna "enclosed area," related to *varros "post." Or the Old French forms may derive from the present participle of Old French warir "defend, keep," from the Germanic root *war- "to protect, guard" (source of Old English warian "take care;" see warrant (n.)). Later especially "piece of land for breeding of rabbits" (c.1400), which led to the transferred sense of "cluster of densely populated living spaces" (1640s).
Warren War·ren (wôr'ən), John Collins. 1778-1856.
American surgeon who gave the first public demonstration (1846) of the use of ether as an anesthetic for a surgical procedure.