In the interplanetary novels of C.S. Lewis (Out of the Silent Planet, Perelandra, and That Hideous Strength), an eldil (plural eldila) was an invisible but detectable guardian spirit of the planet. That is roughly an angel.

Each planet except Earth (the 'Silent Planet') had many of them, and the supreme eldil of the planet was called the Oyarsa. The Oyarsa of the Earth had rebelled against the lord of all eldila, who was called Maleldil.