Stink is about fine? That's nonsense (5)
I believe the answer is:
hokum
'nonsense' is the definition.
(I've seen this before)
'stink is about fine?' is the wordplay.
'stink' becomes 'hum' (I've seen this in other cluesasomething with a bad).
'is about' is an insertion indicator.
'fine?' becomes 'ok' (synonyms).
'hum' placed around 'ok' is 'HOKUM'.
'that's' is the link.
(Other definitions for hokum that I've seen before include "Rubbish" , "Be extremely good (at activity)" , "Meaninglessness" , "Claptrap" , "Hogwash" .)