No-nos (6)
I believe the answer is:
taboos
'no-nos' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for taboos that I've seen before include "Religious or superstitious bans" , "They're forbidden by religion or social custom" , "Prohibitions on things not to be done" , "Superstitious bans or prohibitions" , "Prohibitions buy custom or religion" .)