Not in (3)
I believe the answer is:
out
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not in</span>' is the definition.<br/ ><span class="explanation-format__explanation">('out' is the opposite to 'in')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for out that I've seen before include "Openly gay" , "Dismissed, in cricket" , "not worth considering" , "Free" , "Not indoors" .)