Mark out (6)
I believe the answer is:
define
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mark out</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for define that I've seen before include "Describe accurately" , "State the meaning of" , "Give exact meaning as of a word" , "Demarcate" , "Specify" .)