Synonyms for Embryonic (same or very similar meaning)
WordNet sense 1 (of an organism prior to birth or hatching):
embryologic, embryonalWordNet sense 2 (not yet mature):
immatureWordNet sense 3 (in an early stage of development):
embryoticWordNet sense 4 (being or occurring at an early stage of development):
earlyFrom the ODE community, based on WordNetadd/edit