Small painting's start holding small brush (5)
I believe the answer is:
sweep
'brush' is the definition.
('sweep' can be a synonym of 'brush')
'small painting's start holding small' is the wordplay.
'start' indicates taking the first letters.
'holding' means one lot of letters goes inside another.
'small' becomes 'wee' ('wee' can be similar in meaning to 'small'**).
The first letters of 'small paintings' is 'sp'.
'sp' enclosing 'wee' is 'SWEEP'.
(Other definitions for sweep that I've seen before include "clear" , "Gamble - with brush!" , "Wide scope" , "Dust" , "search" .)