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.

---

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

---

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

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

“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

“And now,” Miss Spink said, “Miriam and I proudly present a new and exciting addendum to our theatrical exposition. Do I see a volunteer?”

From "Coraline" by Neil Gaiman

Related Words

• appendix
• postscript