Check out ancient coin in church (4)
I believe the answer is:
case
'check out' is the definition.
(I've seen this before)
'ancient coin in church' is the wordplay.
'ancient coin' becomes 'as' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
'church' becomes 'ce' (abbreviation for Church of England).
'as' placed inside 'ce' is 'CASE'.
Can you help me to learn more?
(Other definitions for case that I've seen before include "Wine buyer's quantity - dative, for example" , "See 12" , "Judge tries this" , "that paperback lacks?" , "Police investigation" .)