Like an unswept hearth (4)
I believe the answer is:
ashy
'like an unswept hearth' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ashy that I've seen before include "Grey-coloured" , "Leaden" , "What could tray be" , "covered in dust" , "Like burnt remains" .)