Most spooky (7)
I believe the answer is:
eeriest
'most spooky' is the definition.
('eery' can be a synonym of 'spooky')
This is the entire clue.
(Other definitions for eeriest that I've seen before include "Weirdest, I.e., trees are wierd" , "Most ghostly" , "Strangest" , "Most strange and frightening" , "Most weird" .)