de·mon 
/ˈdi:mən/ noun
plural de·mons /ˈdi:mən/ noun [count] 1 : an evil spirit
▪ angels and demons [=devils] 2 informal : a person who has a lot of energy or enthusiasm
▪ She is a demon for work. = She works like a demon. [=she works very hard] — see also speed demon 3 : something that causes a person to have a lot of trouble or unhappiness — usually plural ▪ She spent her whole life battling the demons of drug and alcohol addiction. ▪ He finally was able to face the demons from his unhappy childhood. ▪ his inner demons
▪ angels and demons [=devils]
▪ She is a demon for work. = She works like a demon. [=she works very hard] — see also speed demon
