The definition of a postscript is an additional note or remark tacked on at the end that provides more information or details.
The definition of a supplement is something added to complete a whole or to make up for something that is missing.
A concluding statement to a book, explaining or commenting on its purpose, plan, etc.
Find another word for addendum. In this page you can discover 6 synonyms, antonyms, idiomatic expressions, and related words for addendum, like: postscript, addenda, supplement, postface, amended and annexes.