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

Román would make the decision “based on” a point system that differed from what was laid out in the original request for proposals, according to an addendum sent to the bidders.

From Los Angeles Times ● Sep. 4, 2026

If only he let the scene play a little longer, he’d hear Mufasa’s critical addendum: “There’s more to being king than getting your way all the time.”

From Salon ● Jul. 15, 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

Publishing an addendum to his initial paper, he conceded that the true relativistic limit might be double what he originally proposed.

From "Big Science" by Michael Hiltzik

In addition to the request for increased compensation, Hearn said his list of addenda covers practical matters including travel, accreditation and media arrangements.

From BBC ● Aug. 21, 2026

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

Naturally Father had his own addenda for the meeting.

From "The Poisonwood Bible" by Barbara Kingsolver

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

In the show’s final season, the family patriarch’s heirs struggled to decode penciled-in addendums to his last wishes that were found locked in a safe.

From New York Times ● Jul. 9, 2023

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

From Salon ● Apr. 17, 2023

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 Katharine Prescott Wormeley

Related Words

• appendix
• postscript