n.1 a an evil spirit or devil, esp. one thought to possess a person. b the personification of evil passion.
2 a malignant supernatural being; the Devil.
3 (often attrib.) a forceful, fierce, or skilful performer (a demon on the tennis court; a demon player).
4 a cruel or destructive person.
5 (also daemon) a an inner or attendant spirit; a genius (the demon of creativity). b a supernatural being in ancient Greece.
Phrases and idioms:
demon bowler Cricket a very fast bowler. a demon for work colloq. a person who works strenuously.
Etymology: ME f. med.L demon f. L daemon f. Gk daimon deity