n. A thread or filament; any fine thread-like part of a substance, as a single natural filament of wool, cotton, silk, or asbestos, one of the slender terminal roots of a plant, a drawn-out thread of glass, etc.n. In a collective sense, a filamentous substance; a conglomeration of thread-like tissue, such as exists in animals and plants generally; more generally, any animal, vegetable, or even mineral substance the constituent parts of which may be separated into or used to form threads for textile fabrics or the like: as, muscular or vegetable fiber; the fiber of wool; silk, cotton, or jute fiber; asbestos fiber.n. Figuratively, sinew; strength: as, a man of fiber.n. Material; stuff; quality; character.n. Specifically In anatomy and zoology: A filament; a slender thread-like element, as of muscular or nervous tissue. Most tissues and structures of the body are composed of bundles of fibers. See cut under muscular.n. Fibrous tissue in general.n. very fine processes passing through and seeming to rivet together several concentric laminæ of bone-tissue; perforating fibers.n. The specific name of the beaver, Castor fiber.n. [capitalized] A genus of rodents, of the family Muridæ and subfamily Arvicolinæ, of which the type is the muskrat, musquash, or ondatra of North America, Fiber zibethicus, having a long scaly tail, vertically flattened, and large webbed hind feet. See muskrat.