Oil source seen in Van Gogh's art? (9)
I believe the answer is:
sunflower
I believe this clue is a triple definition!
'oil' is the first definition.
(as in sunflower oil)
'source' is the second definition.
(I have seen 'Source of oil' mean 'sunflower' so perhaps 'source' could also mean 'sunflower')
'seen in van gogh's art?' is the third definition.
(Vincent van Gogh painted sunflowers)
(Other definitions for sunflower that I've seen before include "Very tall bloom whose seeds are used to make margarine" , "seen in Van Gogh's art" , "Tall plant" , "nickname of US State" , "Large golden bloom" .)