Castor and Pollux (6)
I believe the answer is:
gemini
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">castor and pollux</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 gemini that I've seen before include "Twins constellation" , "Heavenly sign of the Twins" , "Castor and Pollux constellation" , "House" , "star group" .)