Definition of "codicil"

So insistent was this demand that the Wyandot actually received a codicil to the treaty […]

2004, Barbara Alice Mann, “The Greenville Treaty of 1795: Pen-and-Ink Witchcraft in the Struggle for the Old Northwest”, in Bruce E. Johansen, editor, Enduring Legacies: Native American Treaties and Contemporary Controversies‎, Praeger, page 155

Those loose ends were tied up in a little-understood clarification of Brexit called the Northern Ireland protocol, ratified in January 2020. It looked like a mere codicil three years ago; now it looks like a serious diplomatic blunder that could threaten Britain’s territory and the region’s peace.

2023 January 26, Christopher Caldwell, “It’s Anyone’s Guess What Will Happen in Northern Ireland in the Next 12 Weeks”, in The New York Times‎

If Nick answered a question Wani listened to him and then gave a flat little codicil or correction.

2004, Alan Hollinghurst, The Line of Beauty […], 1st US edition, New York, N.Y.: Bloomsbury Publishing, page 378