Etymology
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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.
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trailer (n.)
1580s, "hound or huntsman that follows a trail," agent noun from trail (v.). From 1610s as "Something that trails." From 1890 as "vehicle pulled by another;" originally a small carriage drawn along by a bicycle. Meaning "preview of a coming movie" first attested 1928. Trailer park "mobile home community" recorded by 1936. Trailer trash in use by 1986.
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semi-trailer (n.)

also semitrailer, 1910 in reference to motor vehicles (late 19c. in botany), from semi- + trailer. The short form semi is attested by 1942.

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jack-knife (n.)
also jackknife, "pocket knife larger than a pen-knife," 1711, probably American English, apparently from some sense of jack (n.). Perhaps it originally was associated with sailors. Jackleg, jacklegged was a U.S. colloquial term of contempt from 1839. Scottish dialect had jockteleg (1670s) "large clasp-knife," of unknown origin, also jackylegs, jack-o-legs. 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.
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amtrac (n.)
amphibious assault vehicle, 1944, contraction of amphibious tractor (n.).
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backhoe (n.)

"excavating equipment consisting of a digging bucket on the end of an articulated arm, typically mounted on the back of a tractor," by 1928, from back (n. or adj.) + hoe (n.).

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bulldozer (n.)
"person who intimidates others by threats or violence," 1876, agent noun from bulldoze (q.v.). Meaning extended to "an engine-powered ground-clearing caterpillar tractor" in 1930.
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toolbar (n.)

1960 as a frame fitted to a tractor to hold tools; from tool (n.) + bar (n.1). Computer sense is attested from 1991.

Among 100-odd new features in Excel 3.0 is a row of "buttons" on the screen called the Toolbar. Located under the pull-down menus, the Toolbar provides rapid access to frequently used commands. [Popular Science, April 1991.]
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locomotive (adj.)
1610s, "pertaining to movement," from French locomotif, from Latin loco "from a place" (ablative of locus "place;" see locus) + Late Latin motivus "moving" (see motive).

From 1650s as "moving from place to place;" by 1814 as "having the power of moving by itself. The noun meaning "engine which travels on rails by its own power" is from 1829, short for locomotive engine, which is attested from 1814. A locomotive engine used without rails was a traction engine, which became tractor.
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pup (n.)

1760, "young dog," shortened form of puppy (q.v.). Used earlier (from 1580s) for "conceited person," from the figurative sense of puppy. An English-Latin wordbook from late 15c. for Latin pupa gives English pup-bairn. Applied to the young of the fur seal from 1815. Used for "inexperienced person" by 1890.

Pup tent (also dog tent) as a type of small tent used in the military is from 1863. Sopwith pup, popular name of the Sopwith Scout Tractor airplane, is from 1917.

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