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

The launch marks a strategic alignment between the company’s industrial capabilities and the fast-growing wellness sector, positioning the brand for expansion into North and South America. —Jon Stojan, USA Today, 10 Dec. 2025

Though far from any dirt-moving stage, state transportation officials have at least put an Interstate 94 expansion project in Waukesha County on the long road to eventual legislative consideration. —Jim Riccioli, jsonline.com, 10 Dec. 2025

This represents a significant expansion for those who have previously been excluded from HSA participation under these plan types. —Associate News Editor, MSNBC Newsweek, 10 Dec. 2025

Paul is also scouting more properties in South Florida and sees the region as a great spot for film projects and expansion. —Miami Herald Archives, Miami Herald, 10 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