Forces out a painting (6)
I believe the answer is:
fresco
'a painting' is the definition.
(fresco is a kind of painting)
'forces out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'forces' is an anagram of 'FRESCO'.
(Other definitions for fresco that I've seen before include "Mural painted on a wall" , "Picture painted on wet plaster" , "Method of painting on walls" , "Forces (anag) - wall painting" , "Watercolour done on wet plaster" .)