Juan's farewell (5)
I believe the answer is:
adios
'juan's farewell' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for adios that I've seen before include "Goodbye, senor" , "Goodbye (20 across)" , "Good-bye (Sp.)" , "Spanish farewell" , "Goodbye (Spanish)" .)