Costal \Cos"tal\ (k?s"tal), a. [Cf. F. costal. See {Costa}.] 1. (Anat.) Pertaining to the ribs or the sides of the body; as, costal nerves. [1913 Webster] 2. (Bot. & Zool.) Relating to a costa, or rib. [1913 Webster] {Costal cartilage}. See {Cartilage}, and Illust. of {Thorax}. [1913 Webster]