Eye, slangily (6)
I believe the answer is:
peeper
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">eye slangily</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for peeper that I've seen before include "Voyeur" , "Viewer" , "Eye (slang)" .)