Microscope sample
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">microscope sample</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 smear that I've seen before include "Slander - tissue sample used for testing" , "Greasy/sticky mark" , "allegation" , "Spread dirty substance, try to damage reputation" , "sample on slide" .)