Sadly a goner, old Herb (7)
I believe the answer is:
oregano
'herb' is the definition.
(oregano is a kind of herb)
'sadly a goner old' is the wordplay.
'sadly' indicates anagramming the letters.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'a'+'goner'='agoner'
'agoner' anagrammed gives 'oregan'.
'oregan'+'o'='OREGANO'
(Other definitions for oregano that I've seen before include "Aromatic culinary herb" , "food flavouring" , "Sweet-smelling herb" , "Wild marjoram" , "Kitchen herb" .)