Lewis & Short

sēmĭ-dĕus, a, um, adj., half-divine: heroes, i. e. the Argonauts, Stat. Th. 5, 373; called also, reges, id. ib. 3, 518; id. Acnill. 2, 363: parentes, id. Th. 9, 376: Manes, Luc. 9, 7: canes, i. e. Anubis, id. 8, 832 (al. semicanes dei): Dryades, Ov. H. 4, 49: Nymphae semideumque genus, id. Ib. 82; cf.: Silvanus arbiter umbrae Semideumque pecus, i. e. the Pans, Stat. Th. 6, 112.
Hence, subst.

    1. 1. sēmĭ-dĕus, i, m., a demigod: semideique deique, Ov. M. 14, 673; 1, 192.
    2. 2. sēmĭ-dĕa, ae, f., a demigoddess: tres volucres, tres semideae, tres semipuellae, i. e. the Sirens, Aus. Idyll. 11, 21.