Origin and history of locomotive

(plural loci), 1715, "place, spot, locality," from Latin locus "a place, spot; appointed place, position; locality, region, country; degree, rank, order; topic, subject," from Old Latin stlocus, a word of uncertain origin. Used by Latin writers for Greek topos. Mathematical sense by 1750.

late 14c., "something brought forward, a proposition, assertion, or argument" (a sense now obsolete), from Old French motif "will, drive, motivation," noun use of adjective, literally "moving," from Medieval Latin motivus "moving, impelling," from Latin motus "a moving, motion," past participle of movere "to move" (from PIE root *meue- "to push away").

Meaning "that which inwardly moves a person to behave a certain way, mental state or force which induces an action of volition" is from early 15c. Hence "design or object one has in any action."

"something that pulls, that which draws or is used for drawing," 1856, from Modern Latin tractor "that which draws," agent noun from past-participle stem of Latin trahere "to pull, draw" (see tract (n.1)).

Earlier the word was used of a quack device consisting of two metal rods which were supposed to relieve rheumatism (1798, in full Perkins's metallic tractor); this is still the specific sense of the noun in Century Dictionary (1891).

The sense of "an engine or vehicle for pulling wagons or plows" is recorded by 1896, from earlier traction engine (1855) "movable steam engine for dragging heavy loads," also used in agriculture. The meaning "powerful truck for pulling a freight trailer" is by 1926.