Endless ingrained dirt, ghastly (4)
I believe the answer is:
Here is my best explanation:
'ghastly' is the definition.
(I've seen this before)
'endless ingrained dirt' is the wordplay.
'endless' means to remove the last letter.
'ingrained dirt' becomes 'grime' (I've seen this before).
'grime' with its final letter taken off is 'GRIM'.
(Other definitions for grim that I've seen before include "Forbidding harsh and unpleasant", "Unsmiling", "Dour and severe", "looking black", "Severe in appearance", "Stern, cruel", "Resolute", "Serious, gloomy", "Serious; dour" and "Dismal, dour".)