oogonium o·o·go·ni·um (ō'ə-gō'nē-əm)n. pl. o·o·go·ni·ums or o·o·go·ni·a (-nē-ə) The primitive egg mother cell from which the oocytes develop.
A female reproductive structure in certain algae and fungi. It is usually a rounded cell or sac containing one or more oospheres.
A cell that arises from a primordial germ cell and differentiates into an oocyte in the ovary of female animals.