Gaffer possibly sold a half of butter (7)
I believe the answer is:
oldster
'gaffer' is the definition.
(thesaurus)
'possibly sold a half of butter' is the wordplay.
'possibly' indicates anagramming the letters.
'a half of' indicates taking half.
'butter' halved is 'ter'.
'sold' anagrammed gives 'olds'.
'olds'+'ter'='OLDSTER'
(Other definitions for oldster that I've seen before include "Wrinkly" , "codger" , "Greybeard" , "Veteran" , "Senior citizen (colloquial)" .)