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

Name the worry out loud, then choose a small boundary that protects your energy, such as turning off notifications during a demanding task. — Tarot.com, Baltimore Sun, 27 June 2026

The ruptures happened along a boundary between the South American and Caribbean tectonic plates. — Phil Helsel, NBC news, 27 June 2026

Family dynamics, living arrangements and unresolved memories may become more active, prompting discussions about boundaries and responsibilities. — Valerie Mesa, PEOPLE, 26 June 2026

Leaders should model and encourage healthy behaviors, such as boundaries, sleep, exercise and disconnecting after work. — Dana Kellerman, Forbes.com, 26 June 2026

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