thresh v.

*terə-, Proto-Indo-European root meaning "to rub, turn," with derivatives referring to twisting, also to boring, drilling, piercing; and to the rubbing of cereal grain to remove the husks, and thus to threshing.

It forms all or part of: atresia; attorn; attorney; attrition; contour; contrite; detour; detriment; diatribe; drill (v.) "bore a hole;" lithotripsy; return; septentrion; thrash; thread; thresh; throw; threshold; trauma; trepan; tribadism; tribology; tribulation; trite; triticale; triturate; trout; trypsin; tryptophan; turn.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit turah "wounded, hurt;" Greek teirein "to rub, rub away;" Latin terere "to rub, thresh, grind, wear away," tornus "turning lathe;" Old Church Slavonic tiro "to rub;" Lithuanian trinu, trinti "to rub," Old Irish tarathar "borer," Welsh taraw "to strike."

Old English wryhta, wrihta (Northumbrian wyrchta, Kentish werhta) "worker," variant of earlier wyhrta "maker," from wyrcan "to work" (see work (v.)). Now usually in combinations (wheelwright, playwright, etc.) or as a surname. A common West Germanic word; cognate with Old Saxon wurhito, Old Frisian wrichta, Old High German wurhto.

The metathesis of an -r- and a vowel in words from Old English also can be seen in thrash, thresh, third, thirty, bird, wrought, and nostril.

Smith was the general term for a worker in metals, and wright for one who worked in wood, and other materials. Hence, in the later English period, smith (which, in Anglo-Saxon, when used without any characteristic addition, was understood as applying more particularly to the worker in iron,) became the particular name of a blacksmith, and wright of a carpenter, as it is still in Scotland. [Thomas Wright, "Anglo-Saxon and Old English Vocabularies," 1884]