1. any supplement; appendix. 2. a supplement to a will, containing an addition, explanation, modification, etc., of something in the will.
“If there were any rumours flying about later, about this Will or codicil, she might have thought that that was what she’d read in this rather undecipherable handwriting.” “A genuine document,” said Poirot. “But there was also a forged codicil.” — Agatha Christie, Hallowe’en Party, 1969
…so all that’s got to be done is for you to draw up your will complete with codicil so it can’t be re-sinned, and let’s get under way to stop Sefior Carrasco’s heart from breaking. — Miguel de Cervantes, Don Quixote, 1605
Codicil, which entered English in the late 1400s, shares a root with code. Both are derived from the same Latin root, codex meaning “book of laws.”