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

For households in high‑tax states like New York, New Jersey and California — where property taxes and local levies routinely surpass the old limit — this expansion can meaningfully reduce taxable income and boost refunds. —Emma Waldman, Forbes.com, 24 Jan. 2026

Beyond physical expansion, the bank views each new branch as a talent opportunity. —Sheryl Estrada, Fortune, 23 Jan. 2026

Lam’s expansion of the state security apparatus with broader police authority over legislation and businesses also has sharpened a long-running rivalry with the military, which controls extensive commercial interests, analysts said. —Aniruddha Ghosal, Los Angeles Times, 23 Jan. 2026

Generally, spending withheld on the health and human services side involved delaying implementation or expansion of programs planned for 2026 into 2027, Correa said. —Olivia Olander, Chicago Tribune, 23 Jan. 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