Supplement to a will (7)
I believe the answer is:
codicil
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">supplement to a will</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for codicil that I've seen before include "Appendix to a will" , "Will's supplement" , "Will's rider" , "Addition to a will" , "Modifier to will" .)