Soviet leader keeps eastern church in clemency (8)
I believe the answer is:
lenience
'clemency' is the definition.
(thesaurus)
'soviet leader keeps eastern church' is the wordplay.
'soviet leader' becomes 'lenin' (I've seen this before).
'keeps' indicates putting letters inside.
'eastern' becomes 'e'.
'church' becomes 'ce' (abbreviation for Church of England).
'lenin' enclosing 'e' is 'lenien'.
'lenien'+'ce'='LENIENCE'
'in' is the link.
(Other definitions for lenience that I've seen before include "Tolerance" , "Quality of mercy in awarding punishment" , "indulgence" .)