Real Dictionary

devil
countable noun: A devil is an evil spirit.
countable noun: If you refer to someone as a devil, you mean that they do not behave very well but you like them and are not angry with them.
countable noun: You can use devil to emphasize the way you feel about someone. For example, if you call someone a poor devil, you are saying that you feel sorry for them. You can call someone you are fond of but who sometimes annoys or irritates you an old devil or a lit
proper noun: In Judaism, Christianity, and Islam, the Devil is the most powerful evil spirit.

devil in American English
the chief evil spirit, a supernatural being subordinate to, and the foe of, God, and the tempter of human beings; Satan: typically depicted as a man with horns, a tail, and cloven feet
noun: the supreme spirit of evil; Satan

devil in British English
noun: the chief spirit of evil and enemy of God, often represented as the ruler of hell and often depicted as a human figure with horns, cloven hoofs, and tail