Is it ensure, insure, or assure?
1590s, "action of using ladders to scale the walls of a fortified place," from Middle French escalade (16c.) "an assault with ladders on a fortification," from Italian scalata, fem. past participle of scalare "to climb by means of a ladder," from scala "ladder," related to Latin scandere "to climb" (see scan). For initial e-, see especial.