Reduce church work (4)
I believe the answer is:
chop
'reduce' is the definition.
(both can mean to chop)
'church work' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'work' becomes 'op' (common abbreviation for 'opus').
'ch'+'op'='CHOP'
(Other definitions for chop that I've seen before include "Cut into small pieces" , "Thick slice of meat including rib" , "Cut of meat; hack" , "Cut of meat - the sack" , "Cutting blow" .)