The part one hears amiss? (5)
I believe the answer is:
share
'the part' is the definition.
('share' can be a synonym of 'part')
'one hears amiss?' is the wordplay.
'amiss?' indicates an anagram (I've seen 'amiss' mean this).
'hears' with letters rearranged gives 'SHARE'.
(Other definitions for share that I've seen before include "Part, portion" , "Give portion to others" , "Have part-ownership" , "Distribute" , "Portion; plough blade" .)