tractoryoudaoicibaDictYouDict[tractor 词源字典]
tractor: [17] Tractor is one of a large family of English words that come from tractus, the past participle of Latin trahere ‘pull’ (others include abstract [14], attract, contract, detract [15], distract [14], extract [15], retract, subtract, trace, tract [14], tractable [16], traction [17], trait, treat, treatise, and treaty). Tractor itself was originally used in English for a device, invented by the 18th-century American doctor Elisha Perkins, for ‘pulling’ across the surface of the skin, which was supposed to relieve rheumatic pains.

It was not applied to a ‘vehicle for pulling loads’ until the end of the 19th century. From Latin trahere itself come English retreat and train; and drag may go back to the same ultimate source.
=> abstract, attract, contract, detract, distract, extract, retract, retreat, subtract, trace, tract, train, trait, treat, treaty[tractor etymology, tractor origin, 英语词源]
tractor (n.)youdaoicibaDictYouDict
1856, "something that pulls," from Modern Latin tractor "that which draws," agent noun from past participle stem of Latin trahere "to pull, draw" (see tract (n.1)). Earlier used of a quack device consisting of two metal rods which were supposed to relieve rheumatism (1798, in full Perkins's metallic tractor); still the main sense in Century Dictionary (1891).

Sense of "an engine or vehicle for pulling wagons or plows" is recorded by 1896, from earlier traction engine (1859). The meaning "powerful truck for pulling a freight trailer" is first found 1926; tractor-trailer as "combined motor-truck and trailer" is from 1914.