Is it ensure, insure, or assure?
c.1600, from French apanage (13c.), from apaner "to endow with means of subsistence," from Medieval Latin appanare "equip with bread," from ad- "to" (see ad-) + panis "bread" (see food). Originally, provisions made for younger children of royalty. The double -p- restored in French 15c.-16c., in English 17c.