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

• 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

The deployment, North Korea's first major foreign military involvement, represents what Ukraine and its Western allies see as a dangerous expansion of the scope of Russia's war against Ukraine. —Robert Birsel shane Croucher, MSNBC Newsweek, 3 Sep. 2025

Eudia and Haroun used the Summit to announce a major expansion of their AI for Good initiative, investing resources to remove systemic barriers and foster economic mobility and opportunity, especially for Arizona’s underserved communities. —Nick Lichtenberg, Fortune, 3 Sep. 2025

Semafor today announced a major expansion of its live journalism business, anchored by the rapid growth of its flagship World Economy platform, the largest gathering of Fortune 500 CEOs in America. —semafor.com, 3 Sep. 2025

This expansion is made possible through a lead gift from the Maguire Foundation. —Chadd Scott, Forbes.com, 3 Sep. 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