Fiber
late Middle English (in the sense ‘lobe of the liver’, (plural) ‘entrails’): via French from Latin fibra ‘fibre, filament, entrails’.
wiktionary
From French fibre, from Old French, from Latin fibra
etymonline
fiber (n.)
late 14c., fibre "a lobe of the liver," also "entrails," from Medieval Latin fibre, from Latin fibra "a fiber, filament; entrails," which is of uncertain origin, perhaps related to Latin filum "a thread, string" (from PIE root *gwhi- "thread, tendon") or to Latin findere "to split" (from PIE root *bheid- "to split").
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.
