Slips; transparencies (6)
I believe the answer is:
slides
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">slips</span>' is the first definition.<br/ ><span class="explanation-format__explanation">('slide' can be a synonym of 'slip')</span><br/ ><br/ >'<span class="explanation-format__original">transparencies</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(slide is a kind of transparency)</span><br/ ><br/ ></span>
(Other definitions for slides that I've seen before include "Sloping chutes in playgrounds" , "Pieces of glass for study of specimens" , "Pieces of glass under the microscope" , "Sloping chutes in the playground" , "Slips, slithers" .)