Satan is odd if cruel (7)
I believe the answer is:
lucifer
'satan' is the definition.
(I know that satan can be written as Lucifer)
'odd if cruel' is the wordplay.
'odd' indicates an anagram.
'if'+'cruel'='ifcruel'
'ifcruel' with letters rearranged gives 'LUCIFER'.
'is' acts as a link.
(Other definitions for lucifer that I've seen before include "Light" , "striker" , "Rising star" , "Rebellious angel; a match" , "Match - Satan" .)