Lewis : lucus

lucus,³ lūcus, ūs, m., i. q. lux, light: cum primo lucu, at daybreak, Ter. Ad. 5, 3, 56 (dub.; Fleck. and Ussing, luci): noctu lucuque, Varr. L. L. 5, 19, § 99 Müll. (ex conj.; al. noctulucus).