Spooks, spectres (6)
I believe the answer is:
ghosts
This clue is a double definition.
'spooks' is the first definition.
(I know this)
'spectres' is the second definition.
('ghost' can be a synonym of 'spectre')
(Other definitions for ghosts that I've seen before include "Apparitions of a dead people" , "Spectres, wraiths" , "Spirits or apparitions" , "Spooks, spectres" , "Writes for another; Ibsen play" .)