impostor (n.) Look up impostor at Dictionary.com
1580s, from Middle French imposteur (16c.), from Late Latin impostor, agent noun from impostus, collateral form of impositus, past participle of imponere "place upon, impose upon, deceive," from assimilated form of in- "into, in, on, upon" (see in- (2)) + ponere "to put place" (see position (n.)).