Borrowed from Latin lūx (“light”), from Proto-Indo-European *lewk- (“white; light; bright”). Cognates include Ancient Greek λευκός (leukós, “white, blank, light, bright, clear”), Ancient Greek λύκη (lúkē, “light, morning twilight”), Sanskrit रोचते (rocate), Middle Persian 𐭩𐭥𐭬 (rōz, “day”) and Old English lēoht (noun) (English light).