early 15c., dissimulaten, "conceal under false appearances, cause to appear different from the reality," from Latin dissimulatus, past participle of dissimulare "to disguise, hide, conceal, keep secret," from dis- (see dis-) + simulare "to make like, imitate, copy, represent," from stem of similis "like, resembling, of the same kind" (see similar). Intransitive sense of "practice pretense, feign" is from 1796. Related: Dissimulated; dissimulating. Earlier was dissimule (late 14c.), transitive and intransitive, from Old French dissimuler.