fiend

1 ENTRIES FOUND:
fiend /ˈfiːnd/ noun
plural fiends
fiend
/ˈfiːnd/
noun
plural fiends
Britannica Dictionary definition of FIEND
[count]
1 
a  : an evil spirit : a demon or devil
b  : a very evil or cruel person
2 
informal
a  : a person who is very enthusiastic about something : fanatic
b  : a person who is addicted to a drug or to a kind of behavior

like a fiend

chiefly US, informal
— used to say that someone does a lot of something