Herb is awfully arrogant (8)
I believe the answer is:
tarragon
'herb' is the definition.
(I know that tarragon is a type of herb)
'awfully arrogant' is the wordplay.
'awfully' indicates anagramming the letters.
'arrogant' is an anagram of 'TARRAGON'.
'is' acts as a link.
(Other definitions for tarragon that I've seen before include "Fragrant herb" , "Arrogant (anag) - herb" , "Arrogant sort of herb" , "Strangely arrogant herb" , "leaves" .)