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 of boundary

• 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

People in the comments section agreed with the woman and applauded her for setting a boundary with her family. —Meredith Wilshere, PEOPLE, 28 Nov. 2025

This leads to the disappearance of Sa3oud and the blurring of boundaries between illusion and reality. —Nick Vivarelli, Variety, 28 Nov. 2025

The boundary that rolled through South Florida on the holiday pulled down the cooler air. —Scott Withers, CBS News, 28 Nov. 2025

As the boundary between digital and human instruction continues to blur, language learning is becoming more hybrid, more personal and more immersive. —Adam Mills, MSNBC Newsweek, 28 Nov. 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