Source : Webster's Revised Unabridged Dictionary (1913)

Dak \Dak\ (d[add]k or d[aum]k), n. [Hind. [dsdot][=a]k.]
   Post; mail; also, the mail or postal arrangements; -- spelt
   also {dawk}, and {dauk}. [India]

   {Dak boat}, a mail boat. --Percy Smith.

   {Dak bungalow}, a traveler's rest-house at the end of a dak
      stage.

   {To travel by dak}, to travel by relays of palanquins or
      other carriage, as fast as the post along a road.