The Collaborative International Dictionary of English v.0.48:
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]WordNet (r) 3.0 (2006):
costal adj 1: of or relating to or near a rib