Lengthens (7)
I believe the answer is:
extends
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lengthens</span>' is the definition.<br/ ><span class="explanation-format__explanation">(extending is a kind of lengthening)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for extends that I've seen before include "Reaches or stretches out, say the hand of friendship" , "Makes longer" , "Lengthens" , "Stretches out over a distance" , "Enlarges" .)