Source : Webster's Revised Unabridged Dictionary (1913)

Mesoderm \Mes"o*derm\, n. [Meso- + Gr. ? skin.] (Biol.)
   (a) The layer of the blastoderm, between the ectoderm and
       endoderm; mesoblast. See Illust. of {Blastoderm} and
       {Ectoderm}.
   (b) The middle body layer in some invertebrates.
   (c) The middle layer of tissue in some vegetable structures.

Source : WordNet®

mesoderm
     n : the middle germ layer that develops into muscle and bone and
         cartilage and blood and connective tissue [syn: {mesoblast}]