boundary

noun

bound·​ary ˈbau̇n-d(ə-)rē 

plural boundaries

: something that indicates or fixes a limit or extent

Those two trees mark the boundary of our property.

the mountain range that forms the country's northern boundary

boundaryless

ˈbau̇n-d(ə-)rē-ləs 

adjective

boundarylessness noun

Synonyms

• limit
• limitation
• confines
• line

Examples of boundary in a Sentence

Those two trees mark the boundary of our property.

The river forms the country's western boundary.

at the boundary between fact and fiction

You need to set boundaries with your children.

Did he violate the boundaries of the doctor-patient relationship?

Recent Examples on the Web

One of those walls, a massive glass awning-style window, lifts skyward to erase the boundary between indoors and out, revealing a sprawling terrace that feels suspended above the city. —Abby Montanez, Robb Report, 24 Oct. 2025

The team had to clean the fossil to expose the soft, paper-thin clay boundary. —Abhishek Bhardwaj, Interesting Engineering, 24 Oct. 2025

The advanced energy management system elevates the ride experience, allowing users to push boundaries with confidence—whether tackling steep hills, rough paths, or long-distance adventures. —Matt Emma, USA Today, 24 Oct. 2025

People in the post's comment section agreed that once the wedding couple sets a boundary like that, any respectful guest should abide by it. —Rachel Raposas, PEOPLE, 24 Oct. 2025

Word History

Etymology

bound entry 6 + -ary entry 1

First Known Use

1598, in the meaning defined above

Phrases Containing boundary

• boundary layer
• K-T boundary

Kids Definition

boundary

noun

bound·​ary ˈbau̇n-d(ə-)rē 

plural boundaries

: something that points out or shows a limit or end : dividing line

Legal Definition

boundary

noun

bound·​ary

plural boundaries

: a theoretical line that marks the limit of an area of land