Italian bye (4)
I believe the answer is:
ciao
'italian bye' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ciao that I've seen before include "Buongiorno o arrivederci" , "Hi - bye" , "Italian greeting at meeting or parting" , "Hello and goodbye to the Italians" , "Italian salutation" .)