Discharge a member of church (3)
I believe the answer is:
arc
'discharge' is the definition.
(synonyms)
'a member of church' is the wordplay.
'member of church' becomes 'RC' (abbreviation for Roman Catholic).
'a'+'rc'='ARC'
(Other definitions for arc that I've seen before include "Segment of circle" , "less than the complete circuit" , "Half-moon" , "Part of a circle's circumference" , "Curvature" .)