What does addendum mean?
An addendum is additional material appended to a book, report, contract, or other document after that document has been finished. Unlike an appendix, which is usually planned as part of the original work, an addendum responds to something discovered or decided later — a correction, clarification, or new condition — and is attached without altering the main text. The word is most at home in formal settings: lawyers attach addenda to contracts, publishers issue them to correct errors, and professors distribute them to revise course materials. Borrowed directly from Latin, where it means 'a thing to be added,' it entered English in the seventeenth century. Its classical plural is 'addenda,' though 'addendums' is now common. In mathematics, a related term survives: the numbers combined in an addition are called addends. Precise and professional, addendum signals that a document's substance can be extended without rewriting it.
nounAn item of additional material, typically omitted or discovered later, added to a book, document, or contract after its completion.
- A piece of additional material added to a completed book, document, or contract.
- (Mathematics) A quantity to be added to another; more commonly called an addend.
"The publisher issued an addendum correcting several errors in the first edition."
"Before signing, the buyer insisted on an addendum specifying the exact date of possession."
"The professor distributed an addendum to the syllabus clarifying the grading policy."
Both plurals are correct; 'addenda' follows the Latin pattern and remains preferred in formal legal and academic writing, while 'addendums' is common in general usage.
"The revised edition included two addenda covering recent regulatory changes."
In formal Latin grammar, 'addendum' literally means 'the thing to be added' — and in mathematics, the numbers being added together are still called 'addends' today.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of addendum
Addendum comes from the Latin verb 'addere,' meaning 'to add,' formed from 'ad-' (toward) and 'dere' (to give or put). In Latin, 'addendum' is the gerundive — literally 'that which must be added.' English adopted the word in the early seventeenth century, primarily in scholarly and legal writing. It shares this root with the mathematical term 'addend' and with words like 'date' (from 'data,' things given), all descendants of the same Latin verb family.
Related word forms
How addendum is actually used
Addendum is a formal word used chiefly in legal, academic, publishing, and business contexts. The traditional plural is 'addenda' (following Latin), though 'addendums' is widely accepted in modern English. It carries a neutral, professional connotation and is rarely used in casual conversation.
Easily confused with addendum
An appendix is a supplementary section planned as part of the original work, whereas an addendum is material added after the document has been completed.