A thing or things to be added; an appendix.
- Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. (noun) (n.) (noun)
An appendix; something added.
- Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. (noun) (n.) (noun)

Usage examples:

The book was probably a long time in the press, for there are no less than 20 pages of addenda in small print.
- Darwin and Modern Science by A.C. Seward and Others
Then there were " showers,"- linen, stocking, and even a tin one; gifts from her girl friends- cup, face, bath and guest towels; all the tremendous trifles and addenda that go to gladden the chattel- loving heart of a woman.
- The Vertical City by Fannie Hurst
And once more into their attentive ears she poured forth this addenda to her previous narrative.
- A Terrible Secret by May Agnes Fleming