Farewell ( Informal ) (7)
There are a few possibilities for this:
cheerio
(Other definitions for cheerio that I've seen before include "See you" , "Final message" , "good health" , "Say this before drinking" , "An informal hearty goodbye" .)
(Other definitions for bye bye that I've seen before include "Later" , "See you" , "The last word" , "so long!" , "One could well be dismissed with this" .)
(Other definitions for see you that I've seen before include "Casual and informal goodbye" , "Informal kind of au revoir - with visual intent" , "Cheers" , "poker-playing expression?" , "For so long" .)