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

were sent on 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

• border
• borderland
• march

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

But here the focus is on a Black family grappling both with the burdens and privileges of a father’s unique legacy and the difficulty of adapting to changing times and new frontiers of political struggle. —Charles McNulty, Los Angeles Times, 3 June 2025

Now, the next frontier is here: multi-agent systems that operate across entire business functions. —Aytekin Tank, Forbes.com, 3 June 2025

There was money to be made peddling lies about swashbuckling frontier gunfighters across hundreds of miles of telegraph wires to clerks in cities around the country. —Paul Begala, New York Times, 31 May 2025

The Tianwen 2 asteroid-comet probe lifted off on Tuesday (May 28), riding into the final frontier atop a Long March 3B rocket from the Xichang Satellite Launch Center in southwestern China. —Mike Wall, Space.com, 29 May 2025

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