Source : Webster's Revised Unabridged Dictionary (1913)

Impostor \Im*pos"tor\, n. [L. impostor a deceiver, fr. imponere
   to impose upon, deceive. See {Impone}.]
   One who imposes upon others; a person who assumes a character
   or title not his own, for the purpose of deception; a
   pretender. ``The fraudulent impostor foul.'' --Milton.

   Syn: Deceiver; cheat; rogue. See {Deceiver}.

Source : WordNet®

impostor
     n : a person who makes deceitful pretenses [syn: {imposter}, {pretender},
          {fake}, {faker}, {fraud}, {sham}, {shammer}, {pseudo}, {pseud},
          {role player}]