The Collaborative International Dictionary of English v.0.48:

Batman \Bat"man\ (b[a^]t"m[a^]n), n. [Turk. ba[.t]man.]
   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.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Batman \Bat"man\ (b[add]"man or b[a^]t"man), n.; pl. Batmen
   (b[a^]t"men). [F. b[^a]t packsaddle + E. man. Cf.
   Bathorse.]
   A man who has charge of a bathorse and his load. --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

batman
    n 1: an orderly assigned to serve a British military officer