Chiefly (6)
I believe the answer is:
mostly
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">chiefly</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for mostly that I've seen before include "More often than not" , "In the main, nearly all" , "In large part" , "For the greater part; usually" , "Largely" .)