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

Others push legal and ethical boundaries to set themselves up for a career in the private sector after term limits. —Nicole Nixon, Sacbee.com, 11 Jan. 2026

Jeff Klaiber took those things and molded Lehman into an Olympian, at times pushing boundaries and pushing Lehman to the brink. —Andrew Carter, Chicago Tribune, 10 Jan. 2026

Your boundaries are reasonable, and you’re allowed to stand up for them! —Tarot.com, Baltimore Sun, 10 Jan. 2026

For some, participating in budgeting challenges such as the no-buy year can be a great way to set boundaries on your spending and set aside money towards your financial goals. —Adriana Morga, The Orlando Sentinel, 10 Jan. 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