Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sēmĭ-somnus, a, um, and sēmĭ-somnis, e, adj. [somnus], half-asleep, sleepy, drowsy (class.): tibi siccae semisomnae, Plaut. Curc. 1, 2, 22; Cic. Fam. 7, 1, 1; id. Verr. 2, 5, 36, § 95 Zumpt N. cr.; Sall. J. 21, 2; Liv. 9, 24; 9, 37; 25, 39 Drak.; 30, 5 fin.; 37, 20; 40, 15; Tac. A. 1, 51; 4, 25; id. H. 5, 22: sopor, Cael. ap. Quint. 4, 2, 124: cor, Phaedr. 4, 14, 13.
Form semisomnis, Sen. Brev. Vit. 14, 4.