frontier

noun

fron·​tier ˌfrən-ˈtir 

ˈfrən-ˌtir, 

frän-ˈtir, 

ˈfrän-ˌtir 

1

a

: a border between two countries

the frontier between Canada and the U.S.

b

obsolete : a stronghold on a frontier

2

a

: a region that forms the margin of settled or developed territory

an expedition to explore the western frontier

b

: the farthermost limits of knowledge or achievement in a particular subject

frontiers in immunology

c

: a line of division between different or opposed things

… the frontiers separating science and the humanities …

—R. W. Clark

d

: a new field for exploitative or developmental activity

… the brain lies before us as one of the last scientific frontiers here on earth.

—Robert Klitzman

frontier adjective

Synonyms of frontier

• border

Examples of frontier in a Sentence

the frontier between Canada and the U.S.

They were sent on an expedition to explore the western frontier.

Recent Examples on the Web

That captures the frontier models from OpenAI, Anthropic, Google DeepMind, xAI, and a handful of others. —Jason Snyder, Forbes.com, 24 May 2026

The next frontier One of the last times Chris Mosier saw Jason Collins was in 2024, at the Stonewall National Monument in New York City during Pride. —Eryn Mathewson, CNN Money, 24 May 2026

SpaceX is developing Starship to help humanity colonize the moon and Mars, finish deploying its Starlink megaconstellation in Earth orbit and do pretty much everything else the company wants to do in the final frontier. —Mike Wall, Space.com, 22 May 2026

The second dream is the myth of an infinite frontier, which justifies a global American empire. —Literary Hub, 21 May 2026

Word History

Etymology

Middle English fronter, from Anglo-French frountere, fronter, from front

First Known Use

15th century, in the meaning defined at sense 1a

Rhymes for frontier

• adhere
• ameer
• amir
• appear
• arrear
• astir
• austere
• career
• cashier
• cohere
• compere
• emir

Kids Definition

frontier

noun

fron·​tier ˌfrən-ˈti(ə)r  frän- 

1

: a border between two countries

2

a

: a region that forms the edge of the settled part of a country

b

: the outer limits of knowledge or achievement

the frontiers of science

frontier adjective