Say that again? (4)
I believe the answer is:
what
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">say that again?</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for what that I've seen before include "Eh?" , "Interrogatory word" , "Which thing?" , "I beg your pardon" , "That which - come again!" .)