'Thread' is PIE *terh- (to twist) — at its core, a twisted fiber. Same root as 'throw' and 'attrition.'
A thin strand of cotton, nylon, or other material used in sewing or weaving; the spiraling ridge of a screw; a sequence of linked messages or ideas; to pass a thread through something.
From Old English 'þrǣd' (thread, wire, filament), from Proto-Germanic *þrēduz (twisted thing, thread), from *þrēaną (to twist, to turn), from PIE *terh₁- (to twist, to turn, to rub). The word is fundamentally about twisting — a thread is a twisted fiber. The same PIE root produced 'throw' (originally to twist, to turn — as in 'to throw a pot' on a wheel), 'throe' (a twisting pain), and Latin 'terere' (to rub, to wear), giving English 'trite,' 'contrite,' and 'attrition.' Key roots: *þrēduz (Proto-Germanic: "twisted thing, thread"), *þrēaną (Proto-Germanic: "to twist, to turn"), *terh₁- (Proto-Indo-European: "to twist, to turn, to
German 'Draht' (wire) and English 'thread' are the same word — both from Proto-Germanic *þrēduz. But they diverged in meaning: English kept 'thread' for soft textile fiber, while German shifted to mean metal wire. The word 'threadbare' (worn through until the threads show) was originally a literal description of cloth worn so thin