Yardstick (9)
I believe the answer is:
criterion
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">yardstick</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for criterion that I've seen before include "Benchmark - standard" , "Touchstone" , "Standard by which something can be judged" , "Standard, reference point" , "Standard by which to judge" .)