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

Sports features prominently across day one, with JioStar sports and live experiences CEO Ishan Chatterjee examining sport as a platform for fandom, AI and commerce, followed by ICC CEO Sanjog Gupta on cricket’s global expansion and La Liga president Javier Tebas on fan engagement and enforcement. —Naman Ramachandran, Variety, 16 June 2026

When announcing its Ohio manufacturing expansion, Joby explicitly invoked the Wright brothers' legacy in Dayton. —Randy Tucker, USA Today, 15 June 2026

Congolese health authorities have previously said contact tracing has been hampered by community resistance in some areas and by the rapid expansion of the outbreak into new health zones, increasing the workload for surveillance teams. —ABC News, 15 June 2026

Much of this growth has been driven by its global expansion. —Beatrice Nolan, Fortune, 15 June 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