Source : Webster's Revised Unabridged Dictionary (1913)

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

Source : WordNet®

codicil
     n : a supplement to a will; a testamentary instrument intended
         to alter an already executed will