The Collaborative International Dictionary of English v.0.48:

Triploblastic \Trip`lo*blas"tic\, a. [Gr. ? threefold + -blast +
   -ic.] (Biol.)
   Of, pertaining to, or designating, that condition of the ovum
   in which there are three primary germinal layers, or in which
   the blastoderm splits into three layers.
   [1913 Webster]