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

But salmon have no boundaries, and bears in pursuit often wander close enough to count droplets clinging to their fur. —Susan Portnoy, AFAR Media, 3 Oct. 2025

The belt, which marks the boundary between the inner rocky planets and the outer gas giants, is as old as the solar system itself. —Chris Young, Interesting Engineering, 3 Oct. 2025

Prenups force couples to agree on that definition, perhaps even setting terms for an open marriage or other relationship boundaries. —Julia Rodgers, Fortune, 3 Oct. 2025

Against the backdrop of New York’s Hudson Valley, the film explores faith, madness, autonomy, and the fragile boundary between salvation and delusion. —Greg Evans, Deadline, 2 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