No beastly sound being heard (3)
I believe the answer is:
nay
'no' is the definition.
(archaic form 'no')
'beastly sound being heard' is the wordplay.
'beastly sound' becomes 'neigh' (sound of a horse).
'being heard' indicates a 'sounds like' (homophone) clue.
'neigh' is a homophone of 'NAY'.
(Other definitions for nay that I've seen before include "Indeed" , "disagreement" , "In point of fact - a parliamentary vote against" , "Archaic negative" , "No - a negative vote" .)