1a thread or filament from which a vegetable tissue, mineral substance, or textile is formed:the basket comes lined with natural coco fibres
a substance formed of fibres:ordinary synthetics don’t breathe as well as natural fibres [mass noun]:high strength carbon fibre
a thread-like structure forming part of the muscular, nervous, connective, or other tissue in the human or animal body:there were degenerative changes in muscle fibres figurativeshe wanted him with every fibre of her being
(also moral fibre) [mass noun] strength of character:a weak person with no moral fibre
2 [mass noun] dietary material containing substances such as cellulose, lignin, and pectin, that are resistant to the action of digestive enzymes.