Source : Webster's Revised Unabridged Dictionary (1913)

Amercement \A*merce"ment\, n. [OF. amerciment.]
   The infliction of a penalty at the discretion of the court;
   also, a mulct or penalty thus imposed. It differs from a
   fine,in that the latter is, or was originally, a fixed and
   certain sum prescribed by statue for an offense; but an
   amercement is arbitrary. Hence, the act or practice of
   affeering. [See {Affeer}.] --Blackstone.

   Note: This word, in old books, is written amerciament.

   {Amercement royal}, a penalty imposed on an officer for a
      misdemeanor in his office. --Jacobs.