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 ship was retired in 1969, amid the expansion of jet travel and the fall of transatlantic passenger traffic. — Todd C. Frankel, Washington Post, 8 Nov. 2026

However, the researchers propose that nuclear reaction rates and the neutron’s decay rate slow by the same factor, preserving their relationship with the expansion rate. — Rupendra Brahambhatt, Interesting Engineering, 8 Nov. 2026

The backstory The first Mandarin Oriental hotel—then called The Mandarin—opened its doors in Hong Kong in 1963 and has remained central to the hotel group’s core values, despite global expansion. — Condé Nast, Condé Nast Traveler, 7 Nov. 2026

The expansion effort, Simon said, is going well, with the environmental review process getting started. — Graham Womack, Sacbee.com, 7 Nov. 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