un embryonic

An animal in its earliest stage of development, before all the major body structures are represented. In humans, the embryonic stage lasts through the first eight weeks of pregnancy. In humans, other placental mammals, and other viviparous animals, young born as embryos cannot thrive. In marsupials, the young are born during the embryonic stage and complete their development outside the uterus, attached to a teat within the mother's pouch.

The developing young of an egg-laying animal before hatching.

The sporophyte of a plant in its earliest stages of development, such as the miniature, partially developed plant contained within a seed before germination.