Big lie (7)
I believe the answer is:
whopper
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">big lie</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 whopper that I've seen before include "something with no substance in it" , "Enormous lie" , "as related by angler?" , "that 13 [TRUTH SERUM] might detect?" , "large portion?" .)