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

For example, when light bends around a sharp obstacle or boundary, such as a knife edge, the waves bend and interfere with one another to create bands of dark and bright light. — Katie Hunt, CNN Money, 8 Aug. 2026

Homeschool enrichment programs must now comply with a number of new rules, and those that operate outside a district's boundaries need formal approval from the state. — Olivia Young, CBS News, 7 Aug. 2026

The threads are strung the wrong way to hold the boundary together, so the curls grow with nothing to limit them. — Jacek Krywko, ArsTechnica, 7 Aug. 2026

Entering a new regulated market turns into a configuration choice—which region, which controls, which data boundaries—rather than a capital project. — Volodymyr Lebediev, Forbes.com, 7 Aug. 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