Bad breath or containing a bit of niff is noisome (9)
I believe the answer is:
abhorrent
'noisome' is the definition.
(I've seen this before)
'bad breath or containing a bit of niff' is the wordplay.
'bad' is an anagram indicator.
'containing' means one lot of letters goes inside another.
'a bit of' indicates taking the first letters.
The initial letter of 'niff' is 'n'.
'breath'+'or'='breathor'
'breathor' with letters rearranged gives 'abhorret'.
'abhorret' going around 'n' is 'ABHORRENT'.
'is' is the link.
(Other definitions for abhorrent that I've seen before include "Hated" , "Ugly" , "noisome" , "Obscene" , "hateful" .)