Inapt sort of coating (5)
I believe the answer is:
paint
'coating' is the definition.
(paint is a kind of coating)
'inapt sort' is the wordplay.
'sort' is an anagram indicator.
'inapt' is an anagram of 'PAINT'.
'of' is the link.
(Other definitions for paint that I've seen before include "Artist's material" , "A pint of liquid decoration" , "Coloured liquid in tins" , "Surface coating or decoration" , "Coloured coating" .)