tram (n.)

c. 1500, "beam or shaft of a barrow or sledge," also "a barrow or truck body" (1510s), Scottish, originally in reference to the iron trucks used in coal mines. "The further sense development presents many difficulties, chiefly from the scarcity of early examples" [OED, 1989]. It is probably from Middle Flemish tram "beam, handle of a barrow, bar, rung," a North Sea Germanic word of unknown origin. Century Dictionary compares Norwegian tram "edge, brim," Middle Dutch drom "beam, balk," German tram "a beam."

Many recent senses extended from that "wheeled car or wagon used in coal mines." The sense of "track for a wheeled barrow, continuous line of rails (timber, later iron, etc.) used as a tramway" is by 1826; that of "streetcar" is attested by 1879, short for tram-car "car used on a tramway" (1873).

Middle English also had tramme, used of mechanical devices in astronomy and navigating, also "contrivance" generally, from Old French traime and Anglo-Latin trama, from the same source in the "cart-shaft" sense, so called for appearance.