Arrest a public leader in church (5)
I believe the answer is:
pinch
'arrest' is the definition.
(synonyms)
'a public leader in church' is the wordplay.
'leader' says to take the initial letters.
'church' becomes 'ch' (common abbreviation).
The first letter of 'public' is 'p'.
'p'+'in'+'ch'='PINCH'
(Other definitions for pinch that I've seen before include "Squeeze between the fingers" , "appropriate" , "Steal - a little salt, for example" , "amount of salt?" , "Economise - steal" .)