addendum

Concise Oxford English Dictionary © 2008 Oxford University Press:
addendum /əˈdɛndəm/

▶noun (pl. addenda /-də/)

• 1 an extra item added at the end of a book or text.

• 2 Engineering the radial distance from the pitch circle of a cogwheel or wormwheel to the crests of the teeth or ridges. Compare with dedendum.

– origin C17: L., ‘that which is to be added’, gerundive of addere (see add).