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

The additions of Sparling and Keller are part of Scorability’s investment across its engineering, operations and customer success teams. — Sportico Staff, Sportico.com, 7 Aug. 2026

Both said the addition of ABS honed their knowledge of the strike zone, which now varies due to player height rather than stance. — Abby Disalvo, The Orlando Sentinel, 7 Aug. 2026

The series consists of seven books written and illustrated by the Reys from 1941 to 1966, as well as later additions, not by the Reys, commissioned by the publisher Houghton Mifflin Harcourt in the 1990s. — Encyclopedia Britannica, 7 Aug. 2026

In the 1830s, the owners said, the rear wall of the house was expanded to create a saltbox addition. — Kaitlyn Keegan, Hartford Courant, 7 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)