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

Nuclear expansion could drive demand The expected increase in demand is linked in part to US plans to expand domestic nuclear power. — Bojan Stojkovski, Interesting Engineering, 10 Aug. 2026

McLean reported that a previous expansion sold far ahead of schedule, and Fairview said 136 of its 193 independent living units were pre-sold in a little more than a year. — Don Stacom, Hartford Courant, 10 Aug. 2026

Bally's has threatened to sue the city over the potential expansion of video gambling terminals in the city, which the company said is a breach of its contract. — Sara Tenenbaum, CBS News, 10 Aug. 2026

Since the expansion into the province of Quebec in 2023, for instance, gun traces went from 100 to 200 a year to now 4,500 per year, ATF statistics show. — Mark Morales, CNN Money, 9 Aug. 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