demon demon /ˈdiːmən/

noun

1. () An evil supernatural being  ( daemon , daimon , fiend , demon , devil )
   an evil supernatural being
     According to folklore, the demon haunted the abandoned mansion on the hill.
   According to folklore, the demon haunted the abandoned mansion on the hill.
   
   
2. Someone extremely diligent or skillful  ( demon )
   someone extremely diligent or skillful
    He worked like a demon to finish the job on time
   he worked like a demon to finish the job on time
    She's a demon at math
   she's a demon at math
   
3. A cruel wicked and inhuman person  ( demon , devil , monster , fiend , ogre )
   a cruel wicked and inhuman person
     The notorious criminal was known as a fiend for his ruthless acts.
   The notorious criminal was known as a fiend for his ruthless acts.