The Plural of Addendum: Here’s What It Is and How to Use It

Have you ever been trying to talk about more than one addendum and wondered what is the plural form? You have come to the right place. In this article we will talk about what the word addendum means, the verb and plural forms, the history and origin of the word, synonyms, and examples of the word in context. 

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What Is the Definition of Addendum?

The word addendum is defined as:

  • a thing added : ADDITION
  • a supplement to a book  —often used in plural but singular in construction
  • The part of a gear tooth that projects beyond the pitch circle, or the distance that it projects

An addendum is most often used to add something added to the end of a contract as a revision. It can either be used to explain something already stated or to propose a change. To avoid any kind of fraud or confusion, addendums are often a separate signed agreement that is then attached to the original one. The main reason an addendum is used for large documents like a contract is because these documents are so large trying to make changes can be very timely and tedious. It is much easier and productive to simply add in comments, changes, or clarifications to the end. Some examples of documents that would use an addendum are a will, a real estate sales contract, or another form of legal document. This word is different from the word “dedendum” which refers to the radial distance from the pitch line of a cogwheel or worm wheel. 

Addendums, Annexes, and Riders

An addendum is distinguished from other potential additional contract documents as follows:

  • An appendix contains supporting documentation, such as a bank statement, but does not materially alter the terms of the contract.
  • An annex provides additional information, often in the form of a table (such as a tax table) or a standardized form that supplements the contract.
  • A rider is used to add specific provisions or conditions to a standardized contract. Riders are most commonly associated with insurance policies. They may either expand basic coverage (e.g., a homeowner wants a rider attached to their homeowner’s insurance to specifically cover a valuable jewelry collection), or limit coverage (e.g., by excluding coverage for specific medical conditions).
  • Schedules are a type of addendum that deals specifically with numerical information – such as a pricing schedule.
  • Exhibits may be either an addendum, an appendix, or annex. Exhibits provide examples of standard forms or other information that helps one or more parties to a contract clearly understand their obligations under the terms of the contract. 


What Is the Plural Form of Addendum?

When talking about more than one addendum, the correct word becomes addenda. In the English language many words get an “s” on the end to make them plural, but there are some words that still follow the Latin rules like this one. Because there are not many words that still follow the Latin rules some sources use “addendums” as the plural spelling but this however is not correct. If you are having trouble remembering the plural form just remember this unusual word has an unusual plural form. 

The History and Origin of the Word

According to Wiktionary, the singular form addendum dates back to the late 1700s from the Latin word addendum, neuter of addendus, gerundive of addere. Sir James Murray used the singular noun before it was recognized as part of the English language. He used it as a loanword, because he felt it should be officially added into the English language. 

Synonyms of Addendum From a Thesaurus

  • Afterword- a part added at the end of a book or periodical 
    • the author included an afterword about developments in cancer treatment since the book was written
  • Appendix- a part added at the end of a book or periodical 
    • an appendix listing all of the artist’s known works and their current locations
  • Codicil- a part added at the end of a book or periodical 
    • a codicil to the treaty was necessary to clarify certain provisos that had proved to be ambiguous
  • Excursus- a part added at the end of a book or periodical 
    • this biography of Eleanor of Aquitaine contains an interesting excursus on the status of women in the Middle Ages
  • Supplement- something added (as by growth) 
    • this new rule restricting e-mail to job-related activity is only a supplement to the preexisting policy regarding personal use of company resources

Example Sentences of the Word in Context

  • The band has their own Covid addendum to their rider as well and the promoter and venue adhered to all of our requests.

 Billboard, “Smash Mouth Spent ‘Endless Hours’ Making Sure Sturgis Motorcycle Rally Concert Was As Safe As Possible,” 10 Aug. 2020 

  • The interest in the sale was so intense that after the 584-page catalog was printed—and absentee bids began flooding in—the Kennedy children added another 106 lots and an addendum to the catalog was issued.

David Nash, Town & Country, “Jackie Kennedy’s “Lovebird” Clock Reappears After 24 Years,” 18 July 2020 

  • The House released an addendum to the report on Monday that said Bray, a lobbyist for the Arizona Cattle Feeders Association, reported Cook contacted him hours after the lawmaker got a copy of the report.

Andrew Oxford, The Arizona Republic, “Witness in Rep. David Cook investigation says lawmaker sent threatening message,” 29 June 2020 

  • Cook tried calling and later sent a message to Bray that seemed to reference a cattle grazing agreement that Bray has with an Arizona ranch, the addendum said.

Andrew Oxford, The Arizona Republic, “Witness in Rep. David Cook investigation says lawmaker sent threatening message,” 29 June 2020 


The English language can be a tricky thing since it is a compilation of many other languages. Finding the correct plural forms of words is an important step to becoming well educated. Now you are an expert on all things regarding the word of the day, addendum.