The Collaborative International Dictionary of English v.0.48:

Hypoblast \Hy"po*blast\, n. [Pref. hypo- + -blast.] (Biol.)
   The inner or lower layer of the blastoderm; -- called also
   endoderm, entoderm, and sometimes hypoderm. See Illust.
   of Blastoderm, Delamination, and Ectoderm.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Endoderm \En"do*derm\, n. [Endo- + Gr. ? skin.] (Biol.)
   (a) The inner layer of the skin or integument of an animal.
   (b) The innermost layer of the blastoderm and the structures
       derived from it; the hypoblast; the entoblast. See
       Illust. of Ectoderm. Endodermal

WordNet (r) 3.0 (2006):

endoderm
    n 1: the inner germ layer that develops into the lining of the
         digestive and respiratory systems [syn: endoderm,
         entoderm, endoblast, entoblast, hypoblast]