IPA: /ˈkoʊ.dɪ.sɪl/
KK: /ˈkoʊdɪsɪl/
A legal document that adds to or changes a will.
She added a codicil to her will to include her new charity.
Codicil → It is formed from "codi-" (from Latin *codex*, meaning a book or manuscript) and "-cil" (a diminutive suffix). A codicil is a small addition or supplement to a will, akin to a small book or document that modifies the original.
Think of a 'small book' ('codi-') that adds to or modifies a larger document, which helps you remember that a codicil is an addition to a will.
No commonly confused words.