Source : Webster's Revised Unabridged Dictionary (1913)

Extortion \Ex*tor"tion\, n. [F. extorsion.]
   1. The act of extorting; the act or practice of wresting
      anything from a person by force, by threats, or by any
      undue exercise of power; undue exaction; overcharge.

   2. (Law) The offense committed by an officer who corruptly
      claims and takes, as his fee, money, or other thing of
      value, that is not due, or more than is due, or before it
      is due. --Abbott.

   3. That which is extorted or exacted by force.

   Syn: Oppression; rapacity; exaction; overcharge.

Source : WordNet®

extortion
     n 1: an exorbitant charge
     2: unjust exaction (as by the misuse of authority); "the
        extortion by dishonest officials of fees for performing
        their sworn duty"
     3: the felonious act of extorting money (as by threats of
        violence)