Belief of French doctrine (5)
I believe the answer is:
deism
'belief' is the definition.
(I know that Deism is a type of belief)
'of french doctrine' is the wordplay.
'of french' becomes 'de' ('of' in French).
'doctrine' becomes 'ism' (suffix for disciplines or schools of thought).
'de'+'ism'='DEISM'
(Other definitions for deism that I've seen before include "Belief in a god from reason not revelation" , "Belief in a creator" , "Belief in a supreme being who does not intervene in the universe" , "Belief in the existence of God" .)