Fiend arranged no terms (7)
I believe the answer is:
monster
'fiend' is the definition.
(I know that fiend can be written as monster)
'arranged no terms' is the wordplay.
'arranged' indicates anagramming the letters (letters rearranged).
'no'+'terms'='noterms'
'noterms' is an anagram of 'MONSTER'.
(Other definitions for monster that I've seen before include "Huge - beast" , "Large and grotesque animal" , "On terms (anag) - cruel person" , "Inhuman person" , "Large, ugly and frightening imaginary creature" .)