Same word as impostor:

actor, beguiler, bluffer, charlatan, cheat, con artist, deceiver, empiric, fake, faker, four-flusher, fraud, hypocrite, imitator, impersonator, masquerader, mimic, mocker, mountebank, pettifogger, phony, pretender, pseudo, quack, scorner, sham, sharper, shyster, t