"Bye-bye!" (2-2)
'bye-bye' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ta-ta that I've seen before include "Bye!" , "A Farewell" , "Cheerio" , "Adieu" , "Bye-bye" .)
(Other definitions for tata that I've seen before include "So long!" , "See you" , "cheerio!" .)
(Other definitions for see you that I've seen before include "Later we'll meet" , "Cheers" , "Casual and informal goodbye" , "Bye!" , "For so long" .)
(Other definitions for toodle-pip that I've seen before include "so long" , "Take care" , "Farewell remark - dipole top (anag)" , "Goodbye (dated)" , "Farewell (informal)" .)