Clandestine cult trapping endless prey (6)
I believe the answer is:
secret
'clandestine' is the definition.
('secret' can be a synonym of 'clandestine')
'cult trapping endless prey' is the wordplay.
'cult' becomes 'sect' (I've seen this before).
'trapping' means one lot of letters goes inside another.
'endless' says to take the centre.
The central letters of 'prey' are 're'.
'sect' placed around 're' is 'SECRET'.
(Other definitions for secret that I've seen before include "Confidential, not to be revealed" , "hushed prayer" , "Concealed" , "One not to be divulged" , "Not known by others" .)