It reversed the church tax once (5)
I believe the answer is:
tithe
'tax once' is the definition.
(I've seen this before)
'it reversed the' is the wordplay.
'reversed' says the letters should be written in reverse.
'it' written backwards gives 'ti'.
'ti'+'the'='TITHE'
'church' acts as a link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for tithe that I've seen before include "One-tenth; church tax" , "Source of church revenue" , "Levy, originally worth one tenth" , "Impost" , "It used to decimate income" .)