An addendum is an additional item, usually to a document or book. Commonly it includes omissions or other missing material from the original.
The dictionary lists addenda and addendums as recognized plural forms of this word. Addenda is the original Latin plural. However, addendum has been an established English word since the mid-sixteenth century, and as such has taken on the English plural of addendums.
Addendum also has a definition as an Engineering term. It is the radial distance from the pitch circle to the tip of the gear ridge.
Proposed addendum b is one of six addenda to ANSI/ASHRAE Standard 62.1-2013, Ventilation for Acceptable Indoor Air Quality, now open for public comment until Oct. 5, 2014. [ACHR News]
The new edition includes an addendum with activities, frequently asked questions and suggestions for parents on how to maximize the book’s usefulness. [TheraBreath]
You’ll live in footnotes and parentheses, afterthoughts, Scottish addendums to the policies and legalities that will define your future. [Herald Scotland]
Adding to the cumulative burden, many plan sponsors would send physical RFPs, requiring the advisor to retype everything in a Word document, after which the advisor would need to print and mail an entire book, along with multiple addenda, to 7 or 11 committee members. [Think Advisor]
The addendum is how much the gear tooth protrudes outside its pitch diameter. It is specified relative to the tooth spacing. That is, a setting of 0.25 means that a tooth’s addendum will be one quarter of the spacing, or about half of its width. [Woodgears]