amtrac (n.)

1640s, "combining two qualities; having two modes of life," especially "living both on land and in water," from Latinized form of Greek amphibios "having a double life; living on land and in water" (see amphibian (adj.)). Of motor vehicles, from 1915.

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.