Channel extremely briefly captured by religious group (7)
I believe the answer is:
culvert
'channel' is the definition.
(culvert is a kind of channel)
'extremely briefly captured by religious group' is the wordplay.
'extremely' becomes 'very' (I've seen this before).
'briefly' means to remove the last letter.
'captured by' means one lot of letters goes inside another.
'religious group' becomes 'cult' (I've seen this before).
'very' with its last letter removed is 'ver'.
'ver' put inside 'cult' is 'CULVERT'.
(Other definitions for culvert that I've seen before include "Covered drain" , "Conduit" , "Drainage tunnel" , "Tunnel for flow under a road/railway" , "Drain that crosses under a road or path" .)