Is it ensure, insure, or assure?
early 13c., "well-born," from Old French gentil "high-born, noble, of good family" (11c., in Modern French "nice, graceful, pleasing; fine pretty"), from Latin gentilis "of the same family or clan," from gens (genitive gentis) "race, clan," from root of gignere "beget," from PIE root *gen- "produce" (see genus). Sense of "gracious, kind" (now obsolete) first recorded late 13c.; that of "mild, tender" is 1550s. Older sense remains in gentleman.