demon1
  
  n.
    - an evil spirit or devil. 
▸
often humorous an evil or destructive person or thing:
 you little demon.
 - 
[as modifier]
 denoting a person skilful in a specified role:
 a demon cook.
 - another term for daemon1.
 - variant spelling of daemon2.
 
 
  Etymology
  ME: from med. L., from L. daemon (or its dimin. daemonium), from Gk daimōn ‘deity, genius’.
 
  
    
demon2
  
  n.
 Austral./NZ informal a police officer.
 
  Etymology
  C19: perh. from Van Diemen's Land, an early name for Tasmania, or based on dee (sl. term for detective) + man.