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Webster 1913 Edition

Noun.

[L.

codicillus

, dim. of

codex

: cf. F.

codicille

. See

(Law)

A clause added to a will.

Noun.

A writing by way of supplement to a will.

codicil ‎(plural codicils)

(law) An addition or supplement that explains, modifies, or revokes a will or part of one.
- 2005, Alan Hollinghurst, The Line of Beauty, (Bloomsbury Publishing, paperback edition, p. 378)
  If Nick answered a question Wani listened to him and then gave a flat little codicil or correction.

addition made to a will