Is it ensure, insure, or assure?
c.1300, from Old French descendre (10c.) "descend, dismount; fall into; originate in," from Latin descendere "come down, descend, sink," from de- "down" (see de-) + scandere "to climb," from PIE root *skand- "jump" (see scan (v.)). Sense of "originate" is late 14c. in English. Related: Descended; descending.