NOUN (1)

1. a supplement to a will; a testamentary instrument intended to alter an already executed will;

The Collaborative International Dictionary of English v.0.48:

Codicil \Cod"i*cil\, n. [L. codicillus, dim. of codex: cf. F.
   codicille. See Code.] (Law)
   A clause added to a will.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "codicil":
   PS, Parthian shot, addendum, affix, afterthought, allonge,
   appendix, attested copy, back matter, bequeathal, bequest, chorus,
   coda, colophon, commentary, conclusion, consequence, continuance,
   continuation, devise, double take, dying words, enclitic, envoi,
   epilogue, follow-through, follow-up, infix, inheritance,
   interlineation, interpolation, last words, legacy, marginalia,
   note, parting shot, peroration, postface, postfix, postlude,
   postscript, prefix, probate, proclitic, refrain, rider, scholia,
   second thought, sequel, sequela, sequelae, sequelant, sequent,
   sequitur, subscript, suffix, supplement, swan song, tag, tail,
   testament, will