n. A small fiber; a fibrilla; a filament.n. Specifically In botany: One of the delicate cottony hairs or thread-like growths found upon the young rootlets of some plants.n. A rootlet of a lichen.n. One of the filaments which line the utricles of Sphagnum.n. The stipe of some fungi: in this sense disused.n. In histology, a delicate fiber, such as, according to one theory, is found in the protoplasm of cells.