Addenda vs. Addendums – What’s the Difference?

Photo of author


You noticed an error in your newly published article, and you want to edit it. Should you say addendum or addenda? Addenda is the plural of addendum which means a note at the end of an article.

I’ll help you learn when to use addendum and addenda. You’ll also know whether addendums is correct or not, and some sentence examples.

An addendum is an additional item, usually to a document or book. Commonly it includes omissions or other missing material from the original. The dictionary lists addenda and addendums as recognized plural forms of this word. Addenda is the original Latin plural.

When to Use Addendum

Use addendum when referring to a note at the end of an article, book, etc. in the singular form. Authors are most likely to use an addendum when there’s a mistake in a published or sent text. They can also use it for new or forgotten information–for example:

  • Please include an addendum with updates to the first version of the article. 
  • The addendum points out that the author has a new stance on the case. 

A synonym for addendum is supplementary material or appendix. Use it for a revised version f your text. Or if you want to add more materials to your contracts and legal documents. 

When to Use Addenda

Use addenda when you have more than one addendum. This noun is the plural form–for example:

  • The book has ten chapters and addenda.
  • I am proposing addenda to the document draft.
  • Addenda have been added to this insurance contract.
  • Almost all legal contracts have addenda.

Plural nouns typically end with s. But addendum and other words with Latin roots use the Latin rule of replacing -um with -a. Here are other examples:

  • Stratum – strata.
  • Phenomenon – phenomena. 
  • Memorandum – memoranda. 
  • Criterion – criteria. 

Addedums is also a correct plural of addendum. Over time, addendums is becoming popular, but addenda is far more popular so stick with it. 

addenda vs addendums

Using Addenda in a Sentence

Proposed addendum b is one of six addenda to ANSI/ASHRAE Standard 62.1-2013, Ventilation for Acceptable Indoor Air Quality, now open for public comment until Oct. 5, 2014. [ACHR News]

Adding to the cumulative burden, many plan sponsors would send physical RFPs, requiring the advisor to retype everything in a Word document, after which the advisor would need to print and mail an entire book, along with multiple addenda, to 7 or 11 committee members. [Think Advisor]

Using Addendum in a Sentence

The new edition includes an addendum with activities, frequently asked questions, and suggestions for parents on how to maximize the book’s usefulness. [TheraBreath]

You’ll live in footnotes and parentheses, afterthoughts, Scottish addendums to the policies and legalities that will define your future. [Herald Scotland]

The addendum is how much the gear tooth protrudes outside its pitch diameter. It is specified relative to the tooth spacing. That is, a setting of 0.25 means that a tooth’s addendum will be one-quarter of the spacing, or about half of its width. [Woodgears]

How to Remember the Difference Between Addendum vs. Addenda

Usually, you don’t need to remember that addendum is singular, and addenda is the plural form of addendum. Many plural nouns end with -a, such as criteria, bacteria, and memoranda.

But if you still can’t tell the difference, remember that addenda is less popular than addendum. And the less popular word has an unpopular plural form. 

Summary of Addenda vs. Addendum

Addendum and addenda are two different words you cannot substitute for each other.

The noun addendum means a note added to the end of a text or contract law. It’s like supplementary material or an appendix. 

Addenda and addendums are the plural of addendum. But addenda is more recognized and popular. Brush up on other plural forms for your writing such as dice vs die.