Has to (4)
I believe the answer is:
must
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">has to</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 must that I've seen before include "Prerequisite" , "Smell of dampness or staleness" , "The mould is compelled" , "Essential to have" , "Fermenting grape juice" .)