addendum
Americannoun
plural
addenda, addendums-
a thing to be added; an addition.
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an appendix to a book.
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Machinery.
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the radial distance between the tip of a gear tooth and the pitch circle of a gear or the pitch line of a rack.
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Also called addendum circle. an imaginary circle touching the tips of the teeth on a gear.
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noun
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something added; an addition
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a supplement or appendix to a book, magazine, etc
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the radial distance between the major and pitch cylinders of an external screw thread
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the radial distance between the pitch circle and tip of a gear tooth
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.
Vocabulary lists containing addendum
Vocabulary Video Contest (2013) - List 1
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Escape from Mr. Lemoncello's Library
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Thieves' Gambit
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
He said he could have his addendum report completed by 13 March.
From BBC • Feb. 27, 2026
But on Monday, Judge Alice Loke Yee Ching Loke disagreed, saying the royal addendum was not a valid order.
From Barron's • Dec. 22, 2025
His vocal addendum is a wax stamp finalizing the rough-hewn collection of distinct voices.”
From Salon • Jun. 16, 2025
The complaint was added as an addendum to a previous lawsuit against the National Park Service intended to stop the thinning of forests to prevent and lessen the severity of fires.
From Los Angeles Times • Nov. 28, 2023
A loved and cherished addendum, sure, but still an addendum.
From "Pet" by Akwaeke Emezi
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
