addendum

American  

[uh-den-duhm] / əˈdɛn dəm /

noun

addenda, plural addendums plural

1. a thing to be added; an addition.

2. an appendix to a book.

3. Machinery.

   1. the radial distance between the tip of a gear tooth and the pitch circle of a gear or the pitch line of a rack.

   2. Also called addendum circle.  an imaginary circle touching the tips of the teeth on a gear.

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addendum British  

/ əˈdɛndəm /

noun

1. something added; an addition

2. a supplement or appendix to a book, magazine, etc

3. the radial distance between the major and pitch cylinders of an external screw thread

4. the radial distance between the pitch circle and tip of a gear tooth

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Other Word Forms

Noun Inflected Forms

• addenda
  plural
• addendums
  plural

Etymology

Origin of addendum

First recorded in 1785–95; neuter singular of Latin addendus “that which is to be added,” gerundive of addere “to add”; see add

Explanation

When you make an addendum to a document, you are adding text to the end. Addenda tend to be serious business as they're added to contracts, reports, and studies. There is nothing dumb about an addendum; often an addendum makes a document "smarter" by adding more information. If you did a science report on plant growth and found that after your study was complete, the plant flowered in an unusual way, you might describe that as an addendum to your report. Fun fact: the plural of addendum is addenda.

Example Sentences

See Examples For:

addendum addenda addendums

Attorneys can work specific language about dementia care into advance directives, but for many people, having a dementia directive as an addendum is a cost-effective option.

From The Wall Street Journal ● Jul. 3, 2026

An addendum: “It is far easier to work with nobodies or people who are on their way up than established stars.”

From The Wall Street Journal ● Jun. 27, 2026

Out of the blue, we get this settlement, and then when we think we’ve seen it all, we get the addendum.

From Slate ● May 26, 2026

Key in the addendum is that the taxes must have been filed before 19 May, 2026.

From BBC ● May 21, 2026

A loved and cherished addendum, sure, but still an addendum.

From "Pet" by Akwaeke Emezi

The retired brass and veterans organizations added emotionally charged addenda to that legalistic document.

From Los Angeles Times ● Feb. 28, 2025

Teamsters-represented UPS workers are also covered under supplemental agreements, riders and addenda that are specific to the region where they work.

From Reuters ● Apr. 12, 2023

To his right, John Sifton of Human Rights Watch occasionally interjected with incredulous addenda.

From Washington Post ● Feb. 23, 2016

These addenda added immensely to my reading experience.

From Slate ● Aug. 31, 2015

In this section are several addenda to earlier material in this chapter.

From "Innumeracy: Mathematical Illiteracy and Its Consequences" by John Allen Paulos

The eventual pact could look much different from the trilateral agreement that took effect in 2020, perhaps with separate addendums for Canada and Mexico, Shaw added.

From The Wall Street Journal ● Jul. 1, 2026

Three "addendums" remain secret and will only be shared with Ukraine's partners, Zelensky said.

From BBC ● Oct. 16, 2024

Alas, her name isn’t listed among the penciled addendums from unspecified eras.

From Salon ● Apr. 17, 2023

Ertz believes Murray’s love of video games and football can be balanced, no matter what unique addendums are in Murray’s new $230.5 million contract that could keep him in the desert through the 2028 season.

From Seattle Times ● Jul. 26, 2022

Note: The Alkahest is also known as The Quest of the Absolute and is referred to by that title when mentioned in other addendums.

From The Alkahest by Wormeley, Katharine Prescott

Related Words

• appendix
• postscript