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. demon bowler Cricket a very fast bowler. a demon for work colloq. a person who works strenuously.
[ ME f. med.L demon f. L daemon f. Gk daimon deity ]