Giggling butcher chopping head off (8)
I believe the answer is:
laughter
'giggling' is the definition.
'butcher chopping head off' is the wordplay.
'butcher' becomes 'slaughter' (synonyms).
'chopping head off' means to remove the first letter (I've seen 'chopping heads off' mean this).
'slaughter' with its first letter removed is 'LAUGHTER'.
(Other definitions for laughter that I've seen before include "The expression of lively amusement" , "Manifestation of amusement" , "Sign of amusement" , "Guffaws" , "The sound of mirth" .)