Is it ensure, insure, or assure?
1590s, "assembly of people wearing masks and disguises," from French mascarade or Spanish mascarada "masked party or dance," from Italian mascarata "a ball at which masks are worn," variant of mascherata "masquerade," from maschera (see mask (n.)). Figurative sense of "false outward show" is from 1670s.
1650s, from masquerade (n.). Related: Masqueraded; masquerading.