• synonyms


[uh-den-duh m]
noun, plural ad·den·da [uh-den-duh] /əˈdɛn də/ for 1, 2; ad·den·dums for 3.
  1. a thing to be added; an addition.
  2. an appendix to a book.
  3. Machinery.
    1. 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 dedendum.
    2. Also called addendum circle.an imaginary circle touching the tips of the teeth on a gear.
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Origin of addendum

1785–95; neuter singular of Latin addendus to be added, gerundive of addere to add
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words

postscript, appendix, codicil, extension, extra, addition, adjunct, supplement, augmentation, attachment, appendage, rider

Examples from the Web for addendums

Contemporary Examples

Historical Examples

  • He knew how I hated a talkative person, and yet he stampedes into the conversation with his amendments and addendums of syntax.

British Dictionary definitions for addendums


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

C18: from Latin, literally: a thing to be added, neuter gerundive of addere to add
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for addendums



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.

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Online Etymology Dictionary, © 2010 Douglas Harper