Lewis & Short

illūnis (inl-), e, adj. [in-luna], moonless, without moonlight (post-Aug.): nox, Plin. Ep. 6, 20, 14; Sil. 15, 619; Amm. 17, 2, 3.
Also, illūnĭus, a, um: noctis illunio tempore, App. M. 4, p. 150, 29; so, tenebris illuniae caliginis impeditus, id. ib. 9, p. 232, 18.