Source : Webster's Revised Unabridged Dictionary (1913)

Batman \Bat"man\, n. [Turk. batman.]
   A weight used in the East, varying according to the locality;
   in Turkey, the greater batman is about 157 pounds, the lesser
   only a fourth of this; at Aleppo and Smyrna, the batman is 17
   pounds. --Simmonds.

Batman \Bat"man\, n.; pl. {Batmen}. [F. b[^a]t packsaddle + E.
   man. Cf. {Bathorse}.]
   A man who has charge of a bathorse and his load. --Macaulay.

Source : WordNet®

batman
     n : an orderly assigned to serve a British military officer