Octet (9)
I believe the answer is:
eightsome
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">octet</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that octet can be written as eightsome)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for eightsome that I've seen before include "dance!" , "Group of four pairs" , "Reel" , "four groups of parents?" .)