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 stations are standardised, so capacity is added by replicating them, and this line is the blueprint for future local for local expansion. — Prabhat Ranjan Mishra, Interesting Engineering, 27 Sep. 2026

If completed, the expansion would bring the residence to nearly 19,000 square feet. — Abby Montanez, Robb Report, 26 Sep. 2026

Liu cited multiple catalysts that could send the stock higher, ranging from margin expansion to product affordability and rapid expansion. — Michael Bloom, CNBC, 26 Sep. 2026

The new mandate applies to up to 20 million lower-income adults without children at home who are enrolled in Medicaid through an optional expansion in 40 states and the District of Columbia. — ABC News, 26 Sep. 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