/ˈfi:təs ||; ˈfitəs/(US 美 fetus) noun [C] (plural foetuses;fetuses) a young human or animal that is still developing in its mother's body （人或动物的）胎，胎儿 ☞An embryo is at an earlier stage of development. 先有胚胎(embryo)，再发育成胎儿。