addendum

American  

[uh-den-duhm] / əˈdɛn dəm /

noun

plural

addenda, addendums

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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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”; add

Example Sentences

His lawyers had argued that the purported existence of an order by Malaysia's former king, called a "royal addendum", granted him permission to serve the rest of his current sentence at home.

From Barron's • Dec. 22, 2025

“I believe this US Currency is funds from the disposition of the stolen property,” the detective wrote in the warrant addendum.

From Los Angeles Times • Oct. 16, 2025

His vocal addendum is a wax stamp finalizing the rough-hewn collection of distinct voices.”

From Salon • Jun. 16, 2025

But while some hats feel like an addendum to an outfit, others take on more main character energy – as does Melania Trump's today.

From BBC • Jan. 20, 2025

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

Related Words

• appendix
• postscript