Off-limits (5)
I believe the answer is:
taboo
'off-limits' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for taboo that I've seen before include "Not to be touched or used, banned for religious reasons" , "Prohibited as unclean or holy" , "Beyond the pale" , "Ritually forbidden" , "Not permitted" .)