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

• bound
• cap
• ceiling
• confines
• end
• extent
• limit
• limitation
• line
• termination

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

Flynt didn’t hesitate to push boundaries with raw imagery and biting cartoons. —Stephanie Nolasco, FOXNews.com, 22 June 2025

What’s needed now is not just political courage, but real leadership, capable of driving structural reform and aligning finance with planetary boundaries. —Felicia Jackson, Forbes.com, 21 June 2025

Three years later, its entire website is one big collage of young, svelte athletes pushing boundaries in sports like surfing, enduro mountain biking, rock climbing and active-volcano skiing. —New Atlas, 21 June 2025

Thanks to next-gen aircraft, cutting-edge technology, and a surge in demand for seamless international travel, ultra-long-haul flights are pushing the boundaries of modern aviation. —Lauren Dana Ellman, Travel + Leisure, 21 June 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