expansion

noun

ex·​pan·​sion ik-ˈspan(t)-shən 

1

: expanse

2

: the act or process of expanding

territorial expansion

economic expansion

expansion of the universe

3

: the quality or state of being expanded

4

: the increase in volume of working fluid (such as steam) in an engine cylinder after cutoff or in an internal combustion engine after explosion

5

a

: an expanded part

b

: something that results from an act of expanding

The book is an expansion of a lecture series.

6

: the result of carrying out an indicated mathematical operation : the expression of a function in the form of a series

expansional

ik-ˈspan(t)-sh(ə-)nəl 

adjective

Synonyms of expansion

• increase
• boost
• addition
• gain

Examples of expansion in a Sentence

The league is undergoing expansion.

the expansion of a lecture series into a book

This book is an expansion of a lecture series.

Recent Examples on the Web

Under the One Big Beautiful Bill Act, passed and signed into law in July, the agency’s budget soared, allowing a rapid expansion of detention facilities. —Dan Gooding, MSNBC Newsweek, 3 Dec. 2025

Satellite breakups and anti-satellite tests have created an alarming amount of debris, a crisis now exacerbated by the rapid expansion of commercial constellations such as SpaceX’s Starlink. —Mojtaba Akhavan-Tafti, The Conversation, 3 Dec. 2025

About Precision Concepts Precision Concepts’ recent activities have indicated expansion, not downsizing. —Desiree Mathurin december 3, Charlotte Observer, 3 Dec. 2025

American Airlines is partnering with DFW on a multi-billion dollar renovation and expansion of Terminal C, which is expected to be done by 2030. —Matthew Adams, Fort Worth Star-Telegram, 3 Dec. 2025

Word History

First Known Use

1611, in the meaning defined at sense 1

Phrases Containing expansion

• expansion card
• expansion slot

Rhymes for expansion

• mansion
• scansion

Kids Definition

expansion

noun

ex·​pan·​sion ik-ˈspan-chən 

1

: the act of expanding

2

: the state of being expanded

3

: something expanded or a result of expanding

4

: the result of carrying out indicated mathematical operations

the expansion of (a + b)² is a² + 2ab + b²

Medical Definition

expansion

noun

ex·​pan·​sion ik-ˈspan-chən 

1

: the act or process of expanding

2

: the quality or state of being expanded