Seta \Se"ta\ (s[=e]"t[.a]), n.; pl. {Set[ae]} (s[=e]"t[=e]). [L. seta, saeta, a bristle.] 1. (Biol.) Any slender, more or less rigid, bristlelike organ or part; as the hairs of a caterpillar, the slender spines of a crustacean, the hairlike processes of a protozoan, the bristles or stiff hairs on the leaves of some plants, or the pedicel of the capsule of a moss. [1913 Webster] 2. (Zo["o]l.) (a) One of the movable chitinous spines or hooks of an annelid. They usually arise in clusters from muscular capsules, and are used in locomotion and for defense. They are very diverse in form. (b) One of the spinelike feathers at the base of the bill of certain birds. [1913 Webster]