Painting as seen in half of arts magazine (9)
I believe the answer is:
aquarelle
'painting' is the definition.
(I've seen this before)
'as seen in half of arts magazine' is the wordplay.
'as' becomes 'qua' ('qua' is a Latin term meaning 'in the capacity of').
'seen in' indicates putting letters inside.
'half of' means to take half the letters.
'magazine' becomes 'elle' (Elle is a magazine).
'arts' with half the letters taken is 'ar'.
'qua' placed into 'ar' is 'aquar'.
'aquar'+'elle'='AQUARELLE'
(Other definitions for aquarelle that I've seen before include "Painting technique" , "Watercolour" , "in typical Turner style" , "work of art" , "artistic technique" .)