Sweet herb (4)
I believe the answer is:
mint
I believe this clue is a double definition.
'sweet' is the first definition.
(mint is a kind of sweet)
'herb' is the second definition.
(mint is a kind of herb)
(Other definitions for mint that I've seen before include "Plant - in perfect condition" , "Flavour of the money-maker?" , "Aromatic plant; as new" , "Grown in the herb garden" , "sweet herb" .)