Religious group, dry, finally quit (4)
I believe the answer is:
sect
'religious group' is the definition.
(eg a religious sect)
'dry finally quit' is the wordplay.
'dry' becomes 'sec' (similar in meaning).
'finally' says to take the final letters.
The last letter of 'quit' is 't'.
'sec'+'t'='SECT'
(Other definitions for sect that I've seen before include "Heretical group" , "Group, faction" , "Group of people with unusual religious beliefs" , "Nonconformist faction" , "Denomination" .)