Guadalajara goodbye (5)
I believe the answer is:
adios
'guadalajara goodbye' 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 "Adieu, arrivederci" , "Spanish farewell" , "Bye-bye (amigo)" , "so long abroad" , "Goodbye (20 across)" .)