barb - one of the parallel filaments projecting from the main shaft of a feather

cobweb, gossamer - filaments from a cobweb

chromatid - one of two identical strands into which a chromosome splits during mitosis

myofibril, myofibrilla, sarcostyle - one of many contractile filaments that make up a striated muscle fiber

rhizoid - any of various slender filaments that function as roots in mosses and ferns and fungi etc

hypha - any of the threadlike filaments forming the mycelium of a fungus

paraphysis - a sterile simple or branched filament or hair borne among sporangia; may be pointed or clubbed

fiber, fibre - a slender and greatly elongated solid substance