1940s dance (9)
I believe the answer is:
jitterbug
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">1940s dance</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for jitterbug that I've seen before include "Fast, jerky American dance of the 1940s" , "1940s US dance" , "Nervous person" , "Lively jazz dance of the 1940s" .)