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 subsidiary indication.
'endless' means to remove the last letter.
'ingrained dirt' becomes 'grime' (I've seen this before).
'grime' with its final letter taken away is 'grim'.
(Other definitions for grim that I've seen before include "Frightful", "formidable", "Serious; dour", "Severe in appearance", "Dour and severe", "Stern, cruel", "Harshly ironic", "Ironic", "Serious, gloomy" and "Dark, depressing".)