Monocle, basically
I believe the answer is:
lens
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">monocle basically</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lens that I've seen before include "City of northern France: periscope part" , "Device to converge or diverge light" , "town in France" , "Transparent optical device" , "French town" .)