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 city is also participating in the Bartlett Dam expansion project, which could provide a more renewable supply. —Austin Corona, AZCentral.com, 12 Nov. 2025

Equally concerning is the expansion of gang violence toward the peripheral and rural areas of the capital and toward the Artibonite and Center departments. —Jacqueline Charles, Miami Herald, 12 Nov. 2025

Trinity Health Ann Arbor's emergency department will undergo a $60 million renovation and expansion, with construction of the new space to be completed in late 2028. —Christina Hall, Freep.com, 12 Nov. 2025

Over his 27-year career in VFX, Reddy helped shepherd Digital Domain’s international expansion. —Winston Cho, HollywoodReporter, 12 Nov. 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