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

Burpee said the expansion of the State Fair’s cannabis exhibit and lounge seems to reflect changing opinions around marijuana usage in California. — Camila Pedrosa, Sacbee.com, 19 July 2026

County officials have said the additional flights are not an expansion, in part because American, United and other airlines have had commercial flights out of Carlsbad for years in the past. — Phil Diehl, San Diego Union-Tribune, 19 July 2026

China strengthens chemical supply chains Beyond the global tensions driving the project, the expansion reflects China’s broader efforts to reduce emissions in major industrial sectors. — Maria Mocerino, Interesting Engineering, 19 July 2026

Launched in the fall of 2024, the program is now slated for a big expansion. — A.d. Quig, Chicago Tribune, 19 July 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