"Toodle-oo!” (4)
'toodle-oo' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for adieu that I've seen before include "Comment on leaving" , "Gallic goodbye" , "Some say it when leaving" , "Bye" , "Farewell (French)" .)
(Other definitions for tata that I've seen before include "So long!" , "cheerio!" , "See you" .)