The Collaborative International Dictionary of English v.0.48:

Trolley car \Trol"ley car\ (Elec.)
   A motor car powered by electricity drawn from a trolley, and
   thus constrained to follow the trolley lines.
   [Webster 1913 Suppl. +PJC]

   Trolley line,
   (a) A trolley
   (f) .
   (b) The path along which a trolley car runs.
       [PJC]

WordNet (r) 3.0 (2006):

trolley car
    n 1: a wheeled vehicle that runs on rails and is propelled by
         electricity [syn: streetcar, tram, tramcar,
         trolley, trolley car]