Old English gearn "spun fiber, spun wool," from Proto-Germanic *garnan (source also of Old Norse, Old High German, German garn, Middle Dutch gaern, Dutch garen "yarn"), from PIE root *ghere- "intestine, gut, entrail." The phrase to spin a yarn "to tell a story" is first attested 1812, from a sailors' expression, on notion of telling stories while engaged in sedentary work such as yarn-twisting.

*gherə-, Proto-Indo-European root meaning "gut, entrail." 

It forms all or part of: Chordata; chordate; chord (n.2) "structure in animals resembling a string;" chorion; cord; cordon; harpsichord; haruspex; hernia; notochord; yarn.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit hira "vein; band;" Latin hernia "rupture;" Greek khorde "intestine, gut-string;" Lithuanian žarna "guts, leather bag;" Old English gearn, Old High German garn "yarn" (originally made of dried gut), Old Norse gorn "gut."

"ball of thread or yarn," northern English and Scottish relic of Old English cliewen "sphere, ball, skein, ball of thread or yarn," probably from West Germanic *kleuwin (source also of Old Saxon cleuwin, Dutch kluwen), from Proto-Germanic *kliwjo-, perhaps from a PIE *gleu- "gather into a mass, conglomerate," from the source of clay (q.v.). For further sense evolution, see clue (n.).

"fixed quantity of yarn doubled over and over and knotted," early 14c., skaine, from Old French escaigne, escagne (mid-14c., Modern French écagne), a word of uncertain origin. Compare Medieval Latin scagna "a skein," Irish sgainne "a skein, clue."

"action or process of mending a hole (in fabric) by interweaving yarn or thread," 1610s, verbal noun from darn (v.). Darning-needle is from 1848; darning-stitch from 1881.

late 15c., "a kind of thin, worsted wool yarn used in embroidery and fancy work," of unknown origin. Hence crewel-work, kind of embroidery done by crewel, usually upon linen (1849).