a component, as a video card or chip, added to a computer to expand its capabilities.
a small software program that adds a feature to another application.

Nearby words

  1. add,
  2. add fuel to the fire,
  3. add insult to injury,
  4. add up,
  5. add up to,
  6. add-on,
  7. add.,
  8. addams,
  9. addams, charles samuel,
  10. addams, jane

Origin of add-in




verb (used with object)

to unite or join so as to increase the number, quantity, size, or importance: to add two cups of sugar; to add a postscript to her letter; to add insult to injury.
to find the sum of (often followed by up): Add this column of figures. Add up the grocery bills.
to say or write further.
to include (usually followed by in): Don't forget to add in the tip.

verb (used without object)

to perform the arithmetic operation of addition: children learning to add and subtract.
to be or serve as an addition (usually followed by to): His illness added to the family's troubles.


Journalism. copy added to a completed story.

Verb Phrases

add up to, to signify; indicate: The evidence adds up to a case of murder.

Origin of add

1325–75; Middle English adden < Latin addere, equivalent to ad- ad- + -dere to put (combining form; see do1)

Related forms
Can be confusedad add oddaddable edibleadds ads adz Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for add-in



to combine (two or more numbers or quantities) by addition
(tr foll by to) to increase (a number or quantity) by another number or quantity using addition
(tr often foll by to) to join (something) to something else in order to increase the size, quantity, effect, or scope; unite (with)to add insult to injury
(intr foll by to) to have an extra and increased effect (on)her illness added to his worries
(tr) to say or write further
(tr foll by in) to include


informal an instance of adding someone to one's list of contacts on a social networking site, esp MySpaceThanks for the add!
See also add up

Word Origin for add

C14: from Latin addere, literally: to put to, from ad- to + -dere to put


abbreviation for

attention deficit disorder
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 add-in



late 14c., "to join or unite (something to something else)," from Latin addere "add to, join, attach, place upon," from ad- "to" (see ad-) + -dere comb. form meaning "to put, place," from dare "to give" (see date (n.1)). Meaning "to do sums, do addition" also is from late 14c. Related: Added; adding. To add up "make sense" is from 1942.

Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for add-in



attention deficit disorder

The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for add-in


Abbreviation of attention deficit disorder
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.