Source : Webster's Revised Unabridged Dictionary (1913)

Waler \Wal"er\, n. [From Wales, i.e., New South Wales.]
   A horse imported from New South Wales; also, any Australian
   horse. [Colloq.] --Kipling.

   Note: The term originated in India, whither many horses are
         exported from Australia (mostly from New South Wales),
         especially for the use of cavalry.