a person who pretends to be someone else in order to deceive others, especially for fraudulent gain:the charity has warned anyone approached by the impostor to contact police immediately
late 16th century (in early use spelled imposture, and sometimes confused with imposture in meaning): from French imposteur, from late Latin impostor, contraction of impositor, from Latin imponere(see impose)
Impostor can also be spelled imposter: both are correct.
impostor in other Oxford dictionaries
Definition of impostor in the US English dictionary