Ring holder (4,3)
'ring holder' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for best man that I've seen before include "Supporting male actor at a wedding" , "Groom's friend" , "The groom's assistant at a wedding" , "Groom's primary attendant at wedding" , "Important supporting role at a wedding" .)
(Other definitions for finger that I've seen before include "shop" , "Touch; select" , "Index" , "Feel" , "See 24" .)