boundary
Americannoun
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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.
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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.
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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.
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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.
noun
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something that indicates the farthest limit, as of an area; border
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cricket
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the marked limit of the playing area
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a stroke that hits the ball beyond this limit
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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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Related Words
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
Etymology
Origin of boundary
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.
Vocabulary lists containing boundary
Human Geography - Middle School
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Human Geography - High School
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Political Geography - Middle School
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Together, these goals “should nearly eliminate 90% of all untreated flows reaching the coast,” according to Chad McIntosh, U.S. commissioner of the International Boundary and Water Commission.
From The Wall Street Journal • May 4, 2026
However, a shallow seasonal lake near Perkins in southeast Louisiana may represent the first known crater dating to the Younger Dryas Boundary.
From Science Daily • Dec. 19, 2025
The current cycle ends in October, but Mexico so far has delivered less than 30% of what it owes, according to the International Boundary and Water Commission.
From Los Angeles Times • Apr. 11, 2025
Pratt said she was especially concerned about the narrow waterways of Haro Strait, Turn Point and Boundary Pass.
From Seattle Times • Apr. 29, 2024
The landscape ahead began to look familiar—Crescent Beach, Boundary Bay.
From "The Son of Neptune" by Rick Riordan
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
