Inapt sort of coating (5)
I believe the answer is:
paint
'coating' is the definition.
(I know that paint is a type of coating)
'inapt sort' is the wordplay.
'sort' is an anagram indicator.
'inapt' with letters rearranged gives '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" .)