Our word cardinal goes back to the Latin adjective cardinalis, which meant “serving as a hinge.” The root of this word is the noun cardo, meaning “hinge.” Since a hinge is the device on which a door turns, cardo came to mean “something on which a development turns” or “something very important.” Later the Roman Catholic Church used the adjective cardinalis to refer to principal churches and priests and then to mean “a clergyman of the highest rank, next to the pope.” When borrowed into English, cardinalis became cardinal. A cardinal's robes are a deep red color, and this color influenced the naming of the bird whose color was like that of a cardinal's robes.