Lengthier (6)
I believe the answer is:
longer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lengthier</span>' is the definition.<br/ ><span class="explanation-format__explanation">('long' can be a synonym of 'lengthy')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for longer that I've seen before include "Less short" , "Of greater length" , "More extended" , "Of greater duration" , "Measuring greater distance end to end" .)