Look low we hear (4)
I believe the answer is:
mien
'look' is the definition.
(mien means a look or impression)
'low we hear' is the wordplay.
'low' becomes 'mean' (both can mean nasty).
'we hear' indicates a 'sounds like' (homophone) clue.
'mean' sounds like 'MIEN'.
(Other definitions for mien that I've seen before include "Dignified manner" , "A face - maybe mine" , "attitude" , "Appearance, bearing" , "Facial expression sounds miserly" .)