Lewis & Short

in-sŭbĭdus, a, um, adj., stupid, foolish (post-class.), Gell. 19, 9, 9: vultus, Lampr. Commod. 17, 3: scitamenta, Gell. 18, 8, 1.
Comp., Gell. 6, 1, 2; 13, 20, 4.
Adv.: in-sŭbĭdē, stupidly, foolishly (post-class.): aliquid non insubide introspicere, Macr. S. 7, 14, § 3: disserere, Gell. 1, 2, 4.