Piece in G sharp (6)
I believe the answer is:
biting
'sharp' is the definition.
(thesaurus)
'piece in g' is the wordplay.
'piece' becomes 'bit' (synonyms).
'bit'+'in'+'g'='BITING'
(Other definitions for biting that I've seen before include "Sarcastic; very cold" , "Painful or stinging" , "Cold - tart" , "Mordant" , "Caustic or cutting - like teeth?" .)