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

Starlink, operated by SpaceX, has been a major driver of this expansion. —Neetika Walter, Interesting Engineering, 2 Jan. 2026

The month of January is here to serve as a reminder that with expansion there needs to be clarity, and true clarity requires honesty. —Meghan Rose, Glamour, 1 Jan. 2026

And while the state has formally deprioritized freeway expansion, California transportation agencies have plowed forward with new, pricey projects. —Ariane Lange, Sacbee.com, 1 Jan. 2026

Lower-tier cities emerged as crucial growth engines, with third- and fourth-tier markets’ box office contributions reaching a five-year high in 2025, marking three consecutive years of expansion. —Naman Ramachandran, Variety, 1 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