Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
septem-gĕmĭnus, a, um, adj., sevenfold (poet.): Nilus (as having seven mouths), Cat. 11, 7; Verg. A. 6, 800 (cf. the preced. art. and septemplex): Roma (the city of seven hills), Stat. S. 1, 2, 191: septemgemino Roma jugo, id. ib. 4, 1, 6.