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

In that trial, the addition of an mRNA vaccine also showed no new increase in the rate of serious side effects. — CNN Money, 21 Aug. 2026

The addition of HiLight, a multi-coloured LED on the rear of the 11 Pro Fold, is curious. — Ewan Spence, Forbes.com, 21 Aug. 2026

Going from a billion to a trillion takes the addition of 999 billion—or, expressed another way, 999,000 million. — Clara Moskowitz, Scientific American, 21 Aug. 2026

The latter goal is in line with the growing African movement to reduce raw minerals exports in favor of local value addition. — Alexander Onukwue, semafor.com, 21 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)