"Hail," in old Rome (3)
I believe the answer is:
ave
'hail in old rome' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ave that I've seen before include "Latin greeting" , "Hail in graveyard." , "Hail to the old Romans" , "Hail as to Maria" , "Hail as to Caesar" .)