Torment omnivorous nocturnal mammal (6)
I believe the answer is:
badger
I believe this is a double definition.
'torment' is the first definition.
(badgering is a kind of tormenting)
'omnivorous nocturnal mammal' is the second definition.
(badgers are nocturnal and omnivorous)
(Other definitions for badger that I've seen before include "Black and white striped animal" , "protected species" , "Grab Ed from the animal" , "Beast blamed for TB" , "A mammal; harry" .)