Definition - one that assumes false identity or title for the purpose of deception
This word has been spelled in a wide variety of ways over the centuries, although the two most common forms today are impostor and imposter. Take note, however, that imposture generally refers not to a person, but is a different noun, defined either as “the act or practice of deceiving by means of an assumed character or name” or “an instance of imposture.”
What a fast is this, that an impostore or deceyuable person, I cannot tel who, should abstayne from meates, whiche the Lorde hathe created, & yet ware fatte with the fatnes of synnes?
— Thomas Becon, A Potacion or drinkynge for this holi time of lent very cofortable for all penitent synners, 1542