Source : Webster's Revised Unabridged Dictionary (1913)

Ally \Al*ly"\, n.; pl. {Allies}. [See {Ally}, v.]
   1. A relative; a kinsman. [Obs.] --Shak.

   2. One united to another by treaty or league; -- usually
      applied to sovereigns or states; a confederate.

            The English soldiers and their French allies.
                                                  --Macaulay.

   3. Anything associated with another as a helper; an
      auxiliary.

            Science, instead of being the enemy of religion,
            becomes its ally.                     --Buckle.

   4. Anything akin to another by structure, etc.

Source : WordNet®

Allies
     n 1: the alliance of nations that fought the Axis in World War II
          and which (with subsequent additions) signed the charter
          of the United Nations in 1945
     2: in World War I the alliance of Great Britain and France and
        Russia and all the other nations that became allied with
        them in opposing the Central Powers
     3: an alliance of nations joining together to fight a common
        enemy