Herb a Gooner? Possibly (7)
I believe the answer is:
oregano
'herb' is the definition.
(I know that oregano is a type of herb)
'a gooner? possibly' is the wordplay.
'possibly' indicates anagramming the letters.
'a'+'gooner'='agooner'
'agooner' with letters rearranged gives 'OREGANO'.
(Other definitions for oregano that I've seen before include "Herb - a no-goer (anag)" , "Herb used in cookery" , "Pizza herb" , "Dried marjoram" , "aromatic plant" .)