Costa \Cos"ta\ (k[o^]s"t[.a]), n. [L., rib. See Coast.]

1. (Anat.) A rib of an animal or a human being.

2. (Bot.) A rib or vein of a leaf, especially the midrib.

3. (Zo["o]l.)
   (a) The anterior rib in the wing of an insect.
   (b) One of the riblike longitudinal ridges on the exterior of many corals.

Source: Webster's Revised Unabridged Dictionary (1913)