No medic turned fiendish (7)
I believe the answer is:
demonic
'fiendish' is the definition.
('demonic' can be a synonym of 'fiendish')
'no medic turned' is the wordplay.
'turned' indicates an anagram.
'no'+'medic'='nomedic'
'nomedic' is an anagram of 'DEMONIC'.
(Other definitions for demonic that I've seen before include "Inspired as if by a fiend" , "As if possessed by devil" , "Like a devil or evil spirit" , "Dime con (anag.)" , "Wicked" .)