Forces to do a wall painting (6)
I believe the answer is:
fresco
'a wall painting' is the definition.
(fresco is a kind of wall painting)
'forces to do' is the wordplay.
'to do' is an anagram indicator (I've seen 'doing' mean this (doing can mean solving or working out)).
'forces' is an anagram of 'FRESCO'.
(Other definitions for fresco that I've seen before include "Painting done in wet plaster" , "Mural painted on a wall" , "Watercolour done on wet plaster" , "Wall-painting" , "Mural painted on wet plaster" .)