Lewis & Short

antĕ-lūcānus, a, um, adj. [lux], before light, before day (class.; only in prose): ex antelucano tempore, Cic. Fam. 15, 4: gutta roris antelucani, Vulg. Sap. 11, 23: industria, Cic. Tusc. 4, 19, 44: cenae, which continue the whole night until daybreak, id. Cat. 2, 10: lucubratio, Col. 11, 2, 55: spiritus, i. e. ventus, Vitr. 1, 6; so, aurae, Plin. 18, 6, 7, § 2.
Hence, subst.: antĕlūcā-num, i, n., the dawn (eccl. Lat.): doctrinam quasi antelucanum illumino omnibus, I make to shine as the dawn, * Vulg. Eccli. 24, 44.