Average sounding appearance (4)
I believe the answer is:
mien
'appearance' is the definition.
(I've seen this before)
'average sounding' is the wordplay.
'average' becomes 'mean' (type of average).
'sounding' shows a homophone (sound like).
'mean' is a homophone of 'MIEN'.
(Other definitions for mien that I've seen before include "Person's bearing" , "Bearing, demeanour" , "A manner like mine" , "Counterance - mine?" , "Comportment" .)