Gag, wisecrack (4)
I believe the answer is:
joke
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">gag</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that gag is a more specific form of joke)</span><br/ ><br/ >'<span class="explanation-format__original">wisecrack</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for joke that I've seen before include "something in cracker" , "Amusing quip" , "Quip, witticism" , "guy" , "Witticism, jest" .)