Origin and history of tractile

[area], mid-15c., "extent, continued passage or duration," in phrase tract of time "period or lapse of time" (now obsolete), from Latin tractus "course, progress, movement, a train or course, a space drawn out, duration," etymologically "a drawing out or pulling," from stem of trahere "to pull, draw." This is said [Watkins] to be from a PIE root *tragh- "to draw, drag, move" (source also of Slovenian trag "trace, track," Middle Irish tragud "ebb;" perhaps with a variant form *dhragh-; see drag (v.)). Compare trait and trace (n.1).

The meaning "territory, region of indefinite extent, stretch of land or water" in English is recorded by 1550s. Latin tractus also had a sense of "territory, district, region of land." The specific U.S. sense of "plot of land for development" is recorded from 1912; tract housing is attested by 1953.

Also by 1680s in anatomy, in reference to regions of the body having particular functions (digestive, respiratory, etc.).