Clue (1ac) solved - people involved promoting co-operation (10)
I believe the answer is:
ecumenical
'promoting co-operation' is the definition.
I can't tell whether this defines the answer.
'clue 1ac solved people involved' is the wordplay.
'mac' becomes 'ac'.
'solved' indicates anagramming the letters (the anagram must be solved).
'people' becomes 'meni' (I can't justify this - if you can you should believe this answer much more).
'involved' is an insertion indicator.
'clue'+'ac'='clueac'
'clueac' with letters rearranged gives 'ecucal'.
'ecucal' enclosing 'meni' is 'ECUMENICAL'.
Can you help me to learn more?
(Other definitions for ecumenical that I've seen before include "seeking to promote unity" , "of the church" , "trying to promote unity" , "Promoting unity between churches" .)