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

Another 5 million Singapore dollars will be set aside under a separate fund to help tourism businesses expand into new markets and reduce the financial risks of expansion, Fu said. —Sydney Goh, CNBC, 11 May 2026

The playoff expanded from four to 12 teams in 2024, and after decision makers failed to reach an expansion agreement, the CFP will use the same model for the 2026 season. —Maura Carey, Chicago Tribune, 11 May 2026

This expansion of the waiver seems to be mainly about ensuring that all basic software updates are allowed. —ArsTechnica, 11 May 2026

His involvement extended to the third office as well, contributing to the Chicago expansion that Lopez pioneered. —Lyssanoel Frater, USA Today, 11 May 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