Unorthodox religion (4)
I believe the answer is:
cult
'unorthodox religion' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for cult that I've seen before include "Narrow religious sect" , "Strange religious group" , "Unorthodox religion or sect" , "System of religious worship, may be for minority" , "they believe" .)