Source : Webster's Revised Unabridged Dictionary (1913)

Sundowner \Sun"down`er\, n.
   A tramp or vagabond in the Australian bush; -- so called from
   his coming to sheep stations at sunset of ask for supper and
   a bed, when it is too late to work; -- called also {traveler}
   and {swagman} (but not all swagmen are sundowners).

         Sundowners, -- men who loaf about till sunset, and then
         come in with the demand for unrefusable rations.
                                                  --Francis
                                                  Adams.

Source : WordNet®

sundowner
     n 1: a tramp who habitually arrives at sundown
     2: a drink taken at sundown