Farewell toast (7)
I believe the answer is:
cheerio
This clue is a double definition.
'farewell' is the first definition.
(cheerio is a kind of farewell)
'toast' is the second definition.
(I've seen this before)
(Other definitions for cheerio that I've seen before include "Farewell - drinking toast" , "Say this before drinking" , "Expression used when leaving" , "Final message" , "Informal goodbye, sounds blithe" .)