Sorts men out from the fiends (8)
I believe the answer is:
monsters
'the fiends' is the definition.
('monster' can be a synonym of 'fiend')
'sorts men out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'sorts'+'men'='sortsmen'
'sortsmen' anagrammed gives 'MONSTERS'.
'from' acts as a link.
(Other definitions for monsters that I've seen before include "Ugly, terrifying creatures" , "Large imaginary creatures, usually wicked" , "Large and frightening creatures" , "'Imaginary creatures, large and wicked (8)'" , "Giant imaginary creatures" .)