Discover animal sitting on church (5)
I believe the answer is:
catch
'discover' is the definition.
(as in catching someone in the act)
'animal sitting on church' is the wordplay.
'animal' becomes 'cat' (cats are animals).
'sitting on' is a charade indicator (letters next to each other).
'church' becomes 'ch' (common abbreviation).
'cat'+'ch'='CATCH'
(Other definitions for catch that I've seen before include "Apprehend - drawback" , "Understand" , "Something trapped" , "Seize hold of" , "Apprehend - funny song" .)