Ace artist put on new style of knitwear (4)
I believe the answer is:
aran
'style of knitwear' is the definition.
(I've seen this before)
'ace artist put on new' is the wordplay.
'ace' becomes 'a' (abbreviation).
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'put on' means one lot of letters go next to another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'a'+'ra'+'n'='ARAN'
(Other definitions for aran that I've seen before include "Galway Bay isle" , "Irish islands" , "-- Islands; -- sweater" , "traditional type of knitwear" , "Irish style of knitwear" .)