In church, there's plenty of this stuff (5)
I believe the answer is:
cloth
'this stuff' is the definition.
(thesaurus)
'in church there's plenty' is the wordplay.
'in' means one lot of letters goes inside another.
'church' becomes 'ch' (common abbreviation).
'there's plenty' becomes 'lot' (I am not sure about this - if you are sure you should believe this answer much more).
'ch' placed around 'lot' is 'CLOTH'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for cloth that I've seen before include "rag" , "Woven material" , "The clergy" , "Fabric, textile" , "Gingham, say" .)