Lucifer (/ˈljuːsɪfər/ LEW-si-fər) is a name that, according to dictionaries of the English language, refers either to the Devil or to the planet Venus when appearing as the morning star.

As a name for the Devil, the more common meaning in English, "Lucifer" is the rendering of the Hebrew word הֵילֵל‎ in Isaiah (Isaiah 14:12) given in the King James Version of the Bible. The translators of this version took the word from the Latin Vulgate, which translated הֵילֵל by the Latin word lucifer (uncapitalized), meaning "the morning star, the planet Venus", or, as an adjective, "light-bringing".

As a name for the morning star, "Lucifer" is a proper name and is capitalized in English. In Greco-Roman civilization the morning star was also personified and considered a pagan god. At that time the distinction between capitalized and lower-case letters had not yet been invented.