addition

noun

ad·​di·​tion ə-ˈdi-shən 

a-

1

: a part added (as to a building or residential section)

The addition expanded the kitchen.

2

: anything or anyone added : increase

The clerk was a recent addition to the staff.

3

: the act or process of adding

a recipe enhanced by the addition of freshly ground pepper

especially : the operation of combining numbers so as to obtain an equivalent simple quantity

schoolchildren learning about addition and subtraction

4

: direct chemical combination of substances into a single product

see also:

in addition in addition to

Synonyms of addition

• extension
• annex

Examples of addition in a Sentence

The children learned addition and subtraction.

The museum's collection includes several new additions.

Recent Examples on the Web

Add the softened butter a few tablespoons at a time, mixing well after each addition. — ABC News, 15 Aug. 2026

The Mets could end up leaning on similar timeshares heading into next season, perhaps with an addition or two at second base and/or first base who helps in the margins. — Will Sammon, New York Times, 15 Aug. 2026

The idea is less frozen-in-time theme hotel and more modern luxury resort, and the latest room refreshes and restaurant additions have gotten it almost there. — Condé Nast, Condé Nast Traveler, 15 Aug. 2026

Reddit was announced officially as the next addition to the S&P 500, prompting a rally for the social media stock in early trading. — Alex Harring, CNBC, 14 Aug. 2026

Word History

Etymology

Middle English addicioun, borrowed from Anglo-French addicion, borrowed from Latin additiōn-, additiō, from addi-, variant stem of addere "to add" + -tiōn-, -tiō, suffix of action nouns

First Known Use

14th century, in the meaning defined at sense 1

Phrases Containing addition

• in addition
• in addition to

Rhymes for addition

• admission
• ambition
• attrition
• audition
• clinician
• cognition
• coition
• commission
• condition
• contrition
• dentition
• dismission

Kids Definition

addition

noun

ad·​di·​tion ə-ˈdish-ən 

a-

1

: the result of adding : increase

2

: the act, process, or operation of adding

3

: a part added (as to a building)