Third sign of the zodiac (6)
I believe the answer is:
gemini
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">third sign of the zodiac</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 star sign" , "space programme" , "Zodiacal twins" , "Third zodiacal sign" , "May person" .)