Sounds like robust greeting (4)
I believe the answer is:
hail
'greeting' is the definition.
(hail is a kind of greeting)
'sounds like robust' is the wordplay.
'sounds like' shows a homophone (sound like).
'robust' becomes 'hale' (in good health).
'hale' is a homophone of 'HAIL'.
(Other definitions for hail that I've seen before include "Welcome - precipitation" , "cold weather" , "Fall of ice" , "Call from a distance" , "Welcome (icily?)" .)