Is it ensure, insure, or assure?
mid-15c., from Middle French lascivieux or directly from Late Latin lasciviosus (used in a scolding sense by Isidore and other early Church writers), from Latin lascivia "lewdness, playfulness, frolicsomeness, jolity," from lascivus "lewd, playful, frolicsome, wanton," from PIE *las-ko-, from *las- "to be eager, wanton, or unruly" (cf. Sanskrit -lasati "yearns," lasati "plays, frolics," Hittite ilaliya- "to desire, covet," Greek laste "harlot," Old Church Slavonic laska "flattery," Slovak laska "love," Old Irish lainn "greedy," Gothic lustus, Old English lust "lust"). Related: Lasciviously; lasciviousness. In 17c. also with a verbal form, lasciviate.