Main cloak worn by Seurat at first for painting (8)
I believe the answer is:
seascape
'painting' is the definition.
(I know that seascape is a type of landscape painting)
'main cloak worn by seurat at first' is the wordplay.
'main' becomes 'sea' (the main is an old name for the sea).
'cloak' becomes 'cape' (cape is a kind of cloak).
'worn by' indicates putting letters inside (outside letters are worn by those on the inside).
'at first' suggests taking the first letters.
The first letter of 'seurat' is 's'.
'sea'+'cape'='seacape'
'seacape' enclosing 's' is 'SEASCAPE'.
'for' is the link.
(Other definitions for seascape that I've seen before include "Coastal or ocean view" , "Ocean picture" , "Painting - pea cases (anag)" , "Maritime picture" , "Marine view" .)