embryonic

adjective

1 an embryonic chick:

fetal, unborn, unhatched.

▷antonyms mature.

2 the plan is still in its embryonic stages:

rudimentary, undeveloped, unformed, immature, incomplete, incipient, inchoate, just beginning;

fledgling, budding, beginning, potential, nascent, emerging, developing;

early, primary, elementary, germinal.

▷antonyms mature, developed.

embryonic Oxford Dictionary of English