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

Ukraine’s defense industry faces a different R&D equation Buntar’s expansion comes as European defense technology attracts growing investor interest. — Bojan Stojkovski, Interesting Engineering, 11 Oct. 2026

In addition to being the league’s most valuable franchise, the Valkyries now hold the record for the fastest advancement to the Finals for an expansion team, making it to the championship in only their second season. — Sara Germano, Sportico.com, 10 Oct. 2026

The plan is to grow to 100 million in 2028, once a gas-processing expansion is complete. — Jordan Blum, Fortune, 10 Oct. 2026

Burton, a 5-foot-9 guard, was the third overall pick in the 2025 expansion draft. — Ajc Sports, AJC.com, 10 Oct. 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