Ghostly cry (3)
I believe the answer is:
boo
'ghostly cry' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for boo that I've seen before include "Startling utterance" , "Shout in disgust" , "Sound expressing disapproval" , "Show displeasure orally" , "Disapproving jeer" .)