addendum
Americannoun
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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
Other Word Forms
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.
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
It could be difficult to mount a legal challenge to the settlement and its addendum, according to Kautter, who likened the arrangement to a contract between the president and the federal government.
From MarketWatch • May 20, 2026
An addendum to the settlement released by Blanche on Tuesday bars the IRS from pursuing Trump, his family or companies for back tax claims.
From Barron's • May 19, 2026
The sign proclaims something called the Ice Garden, and Celia smiles at the addendum below which contains an apology for any thermal inconvenience.
From "The Night Circus" by Erin Morgenstern
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.
