Unsuitable sort of paint (5)
I believe the answer is:
inapt
'unsuitable' is the definition.
(thesaurus)
'sort of paint' is the wordplay.
'sort of' indicates an anagram.
'paint' anagrammed gives 'INAPT'.
(Other definitions for inapt that I've seen before include "Ill-suited" , "Unsuited" , "Unsuitable - paint (anag)" , "unqualified" , "Not fitting" .)