Codicil
A formal amendment to an existing will, executed with the same formalities as the will itself — signed and witnessed. In the era of quickly regenerated documents, replacing the whole will is usually safer than layering codicils.
What it means
A codicil modifies, adds to, or partially revokes a will without replacing it. Because it must satisfy full execution formalities anyway, and because multiple documents invite inconsistency and contests, modern practice favors executing a fresh will that expressly revokes prior wills and codicils.