What it means
A codicil is a formal document used to make small amendments to an existing will, such as changing an executor, adding a gift, or updating a beneficiary. It must be signed and witnessed with the same formalities as a will under the relevant state or territory legislation. Because a codicil must be read together with the original will, multiple codicils can create confusion. For anything but minor changes, many lawyers recommend making a fresh will instead.
How it's used
Rather than rewrite his entire will, John added a codicil to leave his vintage watch to his nephew.