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

An expansion of either would likely require a change in the formation of the regular-season schedule, with a second bye week being possible, and a later completion date of the season being a certainty. —Mike Jones, New York Times, 28 Feb. 2026

Phase two of the extension, currently slated to open in spring 2027, will continue the line’s westward expansion, adding stations at Beverly Drive and Century City. —Clara Harter, Los Angeles Times, 28 Feb. 2026

Hip-hop as a vehicle, not a cage Robinson’s path shows another form of expansion beyond music. —Kansas City Star, 27 Feb. 2026

However, Palantir’s future growth is driven more by commercial expansion than government contracts alone — but a win here would reinforce its crown as King of defense AI. —Jeff Kilburg, CNBC, 27 Feb. 2026

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