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

As racial boundaries become more fluid, more people of multiracial heritage may come to culturally and politically identify as white. —George Michael, The Conversation, 19 Dec. 2025

Trump, however, went beyond those traditional boundaries. —Bill Barrow, Fortune, 19 Dec. 2025

Photograph by Evelyn Freja A stroke of inspiration led the boundary-pushing vocalist Dee Dee Bridgewater to pair up with the impressionist pianist Bill Charlap. —Richard Brody, New Yorker, 19 Dec. 2025

Resident Playlist is a straightforward medical drama elevated by its execution, including its creators’ interesting choice to tie the narrative to Korea’s birthrate crisis and the expansion of its world past the series’ boundaries. —Kayti Burt, Time, 18 Dec. 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