Herb in duck and orange concoction (7)
I believe the answer is:
oregano
'herb' is the definition.
(I know that oregano is a type of herb)
'duck and orange concoction' is the wordplay.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'and' is a charade indicator (letters next to each other).
'concoction' is an anagram indicator.
'orange' with letters rearranged gives 'regano'.
'o'+'regano'='OREGANO'
'in' is the link.
(Other definitions for oregano that I've seen before include "Sweet-smelling herb" , "leaves for season" , "Kitchen herb" , "Wild marjoram" , "food flavouring" .)