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

The inaugural prize celebrates a sustained and influential body of work from artists who have pushed creative boundaries and developed a clear directorial voice. — Erik Pedersen, Deadline, 21 Sep. 2026

Mike, Jane and their children try to keep things professional, but continually cross personal boundaries because of their agencies’ proximity. — Aramide Tinubu, Variety, 21 Sep. 2026

By hitchhiking on a passing virus, transposons can defy species boundaries and land in a totally new evolutionary setting. — Jake Buehler, Quanta Magazine, 21 Sep. 2026

Among the boundaries that have been breached, according to the new report, are carbon dioxide concentrations, which reached a record 426 parts per million (ppm) because fossil fuel burning had not decreased at nearly the needed pace. — Andrea Thompson, Scientific American, 21 Sep. 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