Plainness (7)
I believe the answer is:
clarity
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">plainness</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for clarity that I've seen before include "Distinctness" , "Limpidness" , "Transparent quality" , "Lucidness" , "Clearness" .)