Sheer or downright (8)
I believe the answer is:
absolute
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">sheer</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >'<span class="explanation-format__original">downright</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for absolute that I've seen before include "Not qualified; total" , "-273.15degC" , "Unrestricted, out-and-out" , "Free from limits, power perhaps" , "Complete, total, without limits" .)