boundary

American  

[baun-duh-ree, -dree] / ˈbaʊn də ri, -dri /

noun

• boundaries
  plural

1. a line or limit where one thing ends and another begins, or something that indicates such a line or limit.

   The ancient wall still serves as the city's outer boundary.

   These studies straddle the boundaries between computational and social sciences.

   Synonyms:

   limit, bound

2. a limit that separates acceptable behavior from unacceptable behavior.

   I'm just looking for a partner who can respect my boundaries.

   Guiding children toward responsible money habits requires setting boundaries.

3. Also called frontier. Mathematics. the collection of all points of a given set having the property that every neighborhood of each point contains points in the set and in the complement of the set.

4. Cricket. a hit in which the ball reaches or crosses the boundary line of the field on one or more bounces, counting four runs for the batsman.

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boundary British  

/ ˈbaʊndərɪ, -drɪ /

noun

1. something that indicates the farthest limit, as of an area; border

2. cricket

   1. the marked limit of the playing area

   2. a stroke that hits the ball beyond this limit

   3. the four runs scored with such a stroke, or the six runs if the ball crosses the boundary without touching the ground

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Synonym Usage

Boundary, border, frontier share the sense of that which divides one entity or political unit from another. Boundary, in reference to a country, city, state, territory, or the like, most often designates a line on a map: boundaries are shown in red. Occasionally, it also refers to a physical feature that marks the agreed-upon line separating two political units: The Niagara River forms part of the boundary between the United States and Canada. Border is more often used than boundary in direct reference to a political dividing line; it may also refer to the region (of, for instance, a country) adjoining the actual line of demarcation: crossing the Mexican border; border towns along the Rio Grande. Frontier may refer to a political dividing line: crossed the Spanish frontier on Tuesday. It may also denote or describe the portion of a country adjoining its border with another country ( towns in the Polish frontier ) or, especially in North America, the most remote settled or occupied parts of a country: the frontier towns of the Great Plains. Frontier, especially in the plural, also refers to the most advanced or newest activities in an area of knowledge or practice: the frontiers of nuclear medicine.

Other Word Forms

Derived Forms

• transboundary
  adjective

Inflected Forms

Nouns

• boundaries
  plural

Etymology

Origin of boundary

First recorded in 1620–30; bound ³ + -ary

Explanation

If you play a sport you are familiar with the term "in bounds," which refers to the boundary, or limits of the playing field that the players must stay within. It is also the outer limits of any space. A boundary is a border and it can be physical, such as a fence between two properties, or abstract, such as a moral boundary that society decides it is wrong to cross. If you have no sense of boundaries, you probably annoy people sometimes by getting too close to them or talking about inappropriate topics. Gustave Flaubert once said, “Earth has its boundaries, but human stupidity is limitless.” A boundary is basically what limits us.

Example Sentences

See Examples For:

boundary boundaries

Dr Lindsay said: "We have identified a number of different fragments that have been incorporated into the retaining wall of Perth Station, for example, and into boundary walls of gardens."

From BBC ● Oct. 11, 2026

Under the arrangement, the federal government would give about an acre on the western boundary of Yosemite National Park’s nearly 750,000-acre expanse, nestled in California’s Sierra Nevada.

From The Wall Street Journal ● Oct. 10, 2026

In fusion physics, the Cordey saddle represents a relatively accessible point along the boundary separating plasma that still needs outside heating from plasma capable of sustaining its own fusion reactions.

From Science Daily ● Oct. 10, 2026

“In the past 20 years, a new social boundary seems to have calcified among people my age,” Walsh wrote.

From Salon ● Sep. 30, 2026

The Retrieval Squad put down just inside the boundary and began an immediate scan for possible hostiles.

From "Artemis Fowl" by Eoin Colfer

But conservationists say that land exchanges have historically been used only to expand the boundaries of federal parkland.

From The Wall Street Journal ● Oct. 10, 2026

It helps you draw boundaries without being held hostage to accusations of selfishness.

From MarketWatch ● Oct. 8, 2026

Carson, 76, is celebrated for works that often cross the boundaries between poetry, fiction and scholarship.

From BBC ● Oct. 8, 2026

"But it really complicates what is actually a fairly fundamental part of being human, which is that you are warm and you love your children and you put in place some boundaries around them."

From BBC ● Oct. 4, 2026

The shock was so enormous that I found my own puny fear of exposure melting into a much larger darker terror that seemed to have no boundaries.

From "Jacob Have I Loved" by Katherine Paterson

Related Words

• barrier
• border
• borderline
• confines
• edge
• frontier
• horizon
• line
• perimeter