Herb that's never been used (4)
I believe the answer is:
mint
'herb' is the definition.
(mint is a kind of herb)
I don't understand how the remainder of the clue works.
(Other definitions for mint that I've seen before include "Culinary herb" , "Vast sum of money" , "and 18 Down: Southern US cocktail" , "Plant - in perfect condition" , "sweet > factory?" .)