Lewis & Short

1. insomnĭum, ĭi, n. [in-somnus], a dream (mostly in plur.).

        1. (α) In sing.: illud haud ambigitur, qualicumque insomnio ipsi fratrique perniciem allatam, Tac. A. 11, 4: per insomnium dicere, in a dream, Arn. 7, 244: ipsa insomnii verba, Macr. Somn. Scip. 1, 3.
        2. (β) In plur., Ter. Eun. 2, 1, 13 Umpfenbach; Tib. 3, 4, 1; Verg. A. 4, 9; 6, 896; Sil. 10, 358; 11, 102; Plin. 18, 12, 30, § 118.