- jack-knife (n.)
[jack-knife 词源字典] - also jackknife, large pocket knife, 1711, probably American English, "perh[aps] associated with some sense of JACK sb.1, but compare jackleg knife" [OED]; see jack + knife (n.). Jackleg was a U.S. colloquial term of contempt from c. 1850. On another theory, so called because it originally was associated with sailors. As a kind of swimming dive, from 1922. As a type of tractor-trailer accident, 1966. Both from the notion of folding, as the knife does.[jack-knife etymology, jack-knife origin, 英语词源]
- tractor (n.)
- 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.
