Addendum

a thing to be added; an addition.
an appendix to a book.
Machinery.

the radial distance between the tip of a gear tooth and the pitch circle of a gear or the pitch line of a rack.
Compare .
Also called addendum circle. an imaginary circle touching the tips of the teeth on a gear.

Contemporary Examples

That felt like cheating, I imagined my own reaction to reading a book and then finding such an addendum at the end.
Speak, Faulty Memory: Why Memoir Writing Is Harder Than You Think Dave Bry April 2, 2013

Instead, the revelation that he had lied was merely an addendum to an incident that had sent a shock through New York City.
Why the DSK Maid Lied Jesse Ellison July 6, 2011

An addendum to this story comes from the aforementioned “best friend” decorator, John Wiltgen.
The Real Grifter of Beverly Hills Diane Dimond September 14, 2011

Hopefully you could include it as an addendum if not actually include it within the article itself.
Renounced Racist Derek Black Speaks Out Caitlin Dickson July 29, 2013

addendum: this article has been updated to include a statement from Barclays, which disputes the story.
The Highest Paid Man on Wall Street William D. Cohan January 8, 2009

Historical Examples

This was an addendum in “the colonel’s own handwriting” and it closed with “pray for me.”
Sons and Fathers Harry Stillwell Edwards

On the other hand the addendum to the book of Judges, chaps.
Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 2 Various

addendum, ad-den′dum, n. a thing to be added: an appendix:—pl.
Chambers’s Twentieth Century Dictionary (part 1 of 4: A-D) Various

It was, however, suggested that as an addendum a summary should be added.
John Redmond’s Last Years Stephen Gwynn

The back of the tooth is defined with a curve swept from some point on the addendum circle i, such as our judgment will dictate.
Watch and Clock Escapements Anonymous

noun (pl) -da (-də)
something added; an addition
a supplement or appendix to a book, magazine, etc
the radial distance between the major and pitch cylinders of an external screw thread
the radial distance between the pitch circle and tip of a gear tooth
n.

1794, literally “something added,” from Latin addendum, neuter of addendus “that which is to be added,” gerundive of addere (see add (v.)). Classical plural form is addenda.