Organic buff, retired Russian banker (7)
I believe the answer is:
natural
'organic' is the definition.
(similar in meaning)
'buff retired russian banker' is the wordplay.
'buff' becomes 'tan' (I've seen this in another clue).
'retired' says the letters should be written backwards.
'russian banker' becomes 'Ural' (Russian river - something with banks).
'tan' backwards is 'nat'.
'nat'+'ural'='NATURAL'
(Other definitions for natural that I've seen before include "character on the staff" , "Innate, inborn" , "Normal; not man-made" , "Inborn, normal ( 7)" , "(In music) neither sharp nor flat" .)