Quadrille (7)
I believe the answer is:
lancers
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">quadrille</span>' is the definition.<br/ ><span class="explanation-format__explanation">(lancers is a kind of quadrille)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lancers that I've seen before include "Quadrille for eight/sixteen pairs" , "Cavalrymen; quadrille" , "Cavalrymen - dance" , "People performing opening acts in theatre" , "Old regiment; dance" .)