Witch's laugh before midnight? (3)
I believe the answer is:
hag
'witch's' is the definition.
(synonyms)
'laugh before midnight?' is the wordplay.
'laugh' becomes 'ha' ().
'before' means one lot of letters go next to another.
'midnight?' becomes 'g' (the middle letter in 'night').
'ha'+'g'='HAG'
(Other definitions for hag that I've seen before include "Old witch-like woman" , "Crone" , "Witch or ugly old woman" .)