Very steep (5)
I believe the answer is:
sheer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">very steep</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 sheer that I've seen before include "Completely" , "Very thin; unmitigated" , "Mere" , "Downright - deviation" , "transparent fabric" .)