Sounds like an average appearance (4)
I believe the answer is:
mien
'appearance' is the definition.
(I've seen this in another clue)
'sounds like an average' is the wordplay.
'sounds like' shows a homophone (sound like).
'an average' becomes 'mean' (type of average).
'mean' sounds like 'MIEN'.
(Other definitions for mien that I've seen before include "Appearance is strangely mine" , "The carriage" , "A countenance like mine" , "Dignified manner" , "Air - look - manner" .)