Word of farewell (7)
I believe the answer is:
cheerio
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">word of farewell</span>' is the definition.<br/ ><span class="explanation-format__explanation">(cheerio is a kind of word of farewell)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for cheerio that I've seen before include "Expression used when leaving" , "Bye-bye" , "Informal farewell" , "Farewell - drinking toast" , "See you" .)