Religious group dry out at last (4)
I believe the answer is:
sect
'religious group' is the definition.
(eg a religious sect)
'dry out at last' is the wordplay.
'dry' becomes 'sec' (similar in meaning).
'at last' indicates one should take the final letters.
The last letter of 'out' is 't'.
'sec'+'t'='SECT'
(Other definitions for sect that I've seen before include "Subdivision of a religion" , "Dissenting body" , "School, faction" , "Small group with own religious beliefs" , "Cult group" .)