a pulley or truck traveling on an overhead track and serving to support and move a suspended object.
3.
a grooved metallic wheel or pulley carried on the end of a pole (trolley pole) by an electric car or locomotive, and held in contact with an overhead conductor, usually a suspended wire (trolley wire), from which it collects the current for the propulsion of the car or locomotive.
4.
any of various devices for collecting current for such a purpose, as a pantograph, or a bowlike structure (bow trolley) sliding along an overhead wire, or a device (underground trolley) for taking current from the underground wire or conductor used by some electric railways.
5.
a small truck or car operated on a track, as in a mine or factory.
1823, in Suffolk dialect, "a cart," especially one with wheels flanged for running on a track (1858), probably from troll (v.) in the sense of "to roll." Sense transferred to "pulley to convey current to a streetcar motor" (1890), then "streetcar drawing power by a trolley" (1891).