a. [ Pref. hypo- + the root of Gr. gi`gnesqai to be born: cf. F. hypogène. ] (Geol.) Formed or crystallized at depths beneath the earth's surface; -- said of granite, gneiss, and other rocks, whose crystallization is believed of have taken place beneath a great thickness of overlying rocks. Opposed to epigene. [ 1913 Webster ]