Catholic Union involved in organising immense movement for Christian unity (9)
I believe the answer is:
ecumenism
'movement for christian unity' is the definition.
I can't judge whether this definition defines the answer.
'catholic union involved in organising immense' is the wordplay.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'union' becomes 'u' (common abbreviation as in 'Trades Union Congress').
'involved in' is an insertion indicator.
'organising' indicates an anagram.
'c'+'u'='cu'
'immense' is an anagram of 'emenism'.
'cu' placed into 'emenism' is 'ECUMENISM'.
Can you help me to learn more?
(Other definitions for ecumenism that I've seen before include "The movement towards worldwide Christian unity" , "Religious movement" , "Movement to promote better understanding between religions" , "Miscue men engaged in movement for Christian unity" , "Movement to unify the Christian churches" .)