Most broad (6)
I believe the answer is:
widest
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">most broad</span>' is the definition.<br/ ><span class="explanation-format__explanation">('wide' can be a synonym of 'broad')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for widest that I've seen before include "Broadest" , "most spacious" , "showing maximal gap between sides" , "Most broad" , "most off target" .)