Downright coarse, after hot letters (8)
I believe the answer is:
thorough
'downright' is the definition.
(I've seen this before)
'coarse after hot letters' is the wordplay.
'coarse' becomes 'rough' (similar in meaning).
'after' says to put letters next to each other.
'letters' indicates anagramming the letters.
'hot' is an anagram of 'tho'.
'rough' put after 'tho' is 'THOROUGH'.
(Other definitions for thorough that I've seen before include "Doing things with great attention to detail" , "Meticulous - exhaustive" , "Total - painstaking - in-depth" , "Paying attention to detail, meticulous" , "Scrupulous in completing work" .)