Sceptic hates it to be otherwise (7)
I believe the answer is:
atheist
'sceptic' is the definition.
(I've seen this before)
'hates it to be otherwise' is the wordplay.
'to be otherwise' indicates an anagram.
'hates'+'it'='hatesit'
'hatesit' is an anagram of 'ATHEIST'.
(Other definitions for atheist that I've seen before include "Unbeliever" , "One denies the existence of a god" , "One disbelieving in the existence of God or gods" , "Sceptic" , "Someone who denies the existence fo God" .)