No terrain curtailed Australian painter (5)
I believe the answer is:
nolan
'australian painter' is the definition.
(artist Sidney Nolan)
'no terrain curtailed' is the wordplay.
'terrain' becomes 'land' (I've seen this before).
'curtailed' means to remove the last letter.
'land' with its last letter taken away is 'lan'.
'no'+'lan'='NOLAN'
(Other definitions for nolan that I've seen before include "Film director - singing sisters" , "Sir Sidney - - , Australian painter" .)