Additional clause (5)
I believe the answer is:
rider
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">additional clause</span>' is the definition.<br/ ><span class="explanation-format__explanation">(additional clause on a contract or agreement)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for rider that I've seen before include "Motorcyclist" , "Condition added to a legislative bill" , "Contractual clause" , "Comment from jury" , "Condition added to something already agreed" .)