Painter estimated to possess importance (8)
I believe the answer is:
interest
'importance' is the definition.
(I've seen this before)
'painter estimated to possess' is the wordplay.
'to possess' says the answer is hidden in the clue.
'INTEREST' is hidden in the letters of 'painter estimated'.
(Other definitions for interest that I've seen before include "Sum of money paid on top of borrowed amount" , "Fascinate" , "Pursuit" , "point of saving?" , "Proceeds" .)