Sightless (5)
I believe the answer is:
blind
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sightless</span>' is the definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for blind that I've seen before include "shade" , "Failing to see" , "Sightless" , "Unobserving" , "In the dark" .)