Superior-sounding greeting (4)
I believe the answer is:
hiya
'greeting' is the definition.
(I know that hiya is a type of greeting)
'superior-sounding' is the wordplay.
'superior' becomes 'higher' (I've seen this before).
'sounding' shows a homophone (sound like).
'higher' sounds like 'HIYA'.
(Other definitions for hiya that I've seen before include "modern form of salve?" , "Hello!" , "Informal greeting" , "Informal 19 across" .)