The Collaborative International Dictionary of English v.0.48:

dump truck \dump" truck`\ n.
   a truck, usually with an open top, the carrying bopdy of
   which can be tilted so as to emptied its contents without
   handling.

   Syn: dumper.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

dump truck
    n 1: truck whose contents can be emptied without handling; the
         front end of the platform can be pneumatically raised so
         that the load is discharged by gravity [syn: dump truck,
         dumper, tipper truck, tipper lorry, tip truck,
         tipper]