Source : Webster's Revised Unabridged Dictionary (1913)

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 : WordNet®

costa
     n 1: a riblike part of a plant or animal (such as a middle rib of
          a leaf or a thickened vein of an insect wing)
     2: any of the 12 pairs of curved arches of bone extending from
        the spine to or toward the sternum in humans (and similar
        bones in most vertebrates) [syn: {rib}]
     [also: {costae} (pl)]