Ghostly quality (8)
I believe the answer is:
eeriness
'ghostly quality' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for eeriness that I've seen before include "'Ghostliness, scariness (8)'" , "Horror movie featuring such" , "Ghostly atmosphere" , "Is serene (anag.)" , "Weird quality" .)