Entry 1 sense Webster, 1913 Epiblast · Ep·i·blast · IPA 01 n. The outer layer of the blastoderm; the ectoderm. See Blastoderm, Delamination. 1. The outer layer of the blastoderm; the ectoderm. See Blastoderm, Delamination.(Biol.) See: Blastoderm, Delamination