1580s, "to entangle, become entwined confusedly," also "to untangle, disentangle, unwind" (originally with out), from Dutch ravelen "to tangle, fray," rafelen "to unweave," from rafel "frayed thread," which is of uncertain origin. The seemingly contradictory senses of this word (ravel and unravel are both synonyms and antonyms) might be reconciled by its roots in weaving and sewing: as threads become unwoven, they get tangled. The "entangling" meaning is the "more original" sense according to OED. From 1590s in the figurative sense of "make plain or clear;" 1610s as "make a minute and careful investigation." The intransitive sense, of fabric, "become untwisted or disjointed thread from thread" is by 1610s.
Meaning "thread-like structure in animal bodies" is from c. 1600 (in plants, 1660s); hence figurative use in reference to force or toughness (1630s). As "textile material," 1827. Fiberboard is from 1897; Fiberglas is attested from 1937, U.S. registered trademark name; in generic use, with lower-case f- and double -s, by 1941. Fiber optics is from 1956.
1650s, "a drawing of the outline of anything," especially "a representation of the human face in side view," from older Italian profilo "a drawing in outline," from profilare "to draw in outline," from pro "forth" (from PIE root *per- (1) "forward") + filare "draw out, spin," from Late Latin filare "to spin, draw out a line," from filum "thread" (from PIE root *gwhi- "thread, tendon"). Meaning "a side view" is from 1660s. Meaning "biographical sketch, character study" is from 1734.
"knit with inverted stitches," 1825; earlier "embroider with gold or silver thread" (1520s), probably from Middle English pirlyng "revolving, twisting," of unknown origin. The two senses usually are taken as one word, but even this is not certain. Klein suggests a source in Italian pirolare "to twirl," from pirolo "top." As a noun, from late 14c. as "bordering, frills;" 1530s as "twisted thread of gold and silver."
"narrow passage in a mountain region," 1640s, especially in a military sense, "a narrow passage down which troops can march only in single file," from French défilé, noun use of past participle of défiler "march by files" (17c.), from de- "off" (see de-) + file "row," from Latin filum "thread" (from PIE root *gwhi- "thread, tendon"). The verb, "to march off in a line or file," is by 1705, from French défiler.
"thin, stiff, transparent dress fabric," 1820, from French organsin (1660s), and Italian organzino, a strong kind of silk thread, a word of unknown origin; perhaps from the same source as organdy.
"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.
combining form in scientific words, from Greek nēma "thread" (genitive nēmatos), from stem of nein "to spin," from PIE root *(s)ne- "to sew, to spin" (see needle (n.)).