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

This year, Spirit Halloween is extending over 20 contracts to support the expansion of Spirit Christmas, now entering its second year. —Victoria Moorwood, Cincinnati Enquirer, 23 Oct. 2025

Arcade said that as Chairman, Cory will lead the expansion of The Sidemen’s activities. —Stewart Clarke, Deadline, 22 Oct. 2025

The outpost comes amid Salomon’s North America expansion, which includes a total of four brick-and-mortar shops with another shop expected to open by year’s end. —Chris Gardner, HollywoodReporter, 22 Oct. 2025

At the Gateway Arch, a tram ride to the top offered sweeping views of the Mississippi River and downtown, while the museum below traced the city’s role in westward expansion. —Okla Jones, Essence, 22 Oct. 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