Thin covering layer (4)
I believe the answer is:
film
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">thin covering layer</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for film that I've seen before include "Veil; cinema attraction" , "Cinema entertainment" , "Cinema celebrity" , "An entertainment; thin layer" , "Thin layer - seen on screens" .)