Smart reply (6)
(Other definitions for retort that I've seen before include "may be found in lab" , "A quick, sharp reply" , "Lab. vessel; quip" , "A sharp reply or vessel used in distilling" , "Witty reply" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">smart reply</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for riposte that I've seen before include "Rejoinder" , "Sally" , "Snappy comeback" , "Witty retort" , "Reply, response" .)