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

And while the name has changed and updates and expansions have been made over the decades, the soul and aesthetics of the original still come through. —Condé Nast, Condé Nast Traveler, 21 Feb. 2026

Stopping a further expansion of NATO was one of the main reasons Russian officials said the invasion in Ukraine was launched in the first place. —Matthew Chance, CNN Money, 21 Feb. 2026

This will be followed by Los Angeles, the Bay Area, Chicago, Houston, Washington, DC and a New York expansion on March 27 before a wide break in the top 50 North American markets on April 3. —Anthony D'alessandro, Deadline, 20 Feb. 2026

Celsius also touted its partnership with PepsiCo, allowing annual contract value to double, enhanced execution and international expansion as a significant long-term opportunity. —Liz Napolitano, CNBC, 20 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