Defeat hearing defect (5)
I believe the answer is:
floor
'defeat' is the definition.
(e.g. knock to the ground in a fight)
'hearing defect' is the wordplay.
'hearing' shows a homophone (sound like).
'defect' becomes 'flaw' ('flaw' can be a synonym of 'defect').
'flaw' is a homophone of 'FLOOR'.
(Other definitions for floor that I've seen before include "Building's base" , "Dumbfound" , "Sea bottom; baffle" , "Knock down - planking" , "Base of room - storey" .)