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

The real story is that another frontier artificial intelligence company after Anthropic has concluded that law is important enough to become part of a much larger intelligence platform. — Joseph Andrew, Forbes.com, 29 June 2026

Palantir's customers are acknowledging this overlap with frontier AI on products like data mapping and graphing and are moving to take advantage of it. — Tobias Burns, CNBC, 29 June 2026

This latest milestone highlights deep-sea offshore wind as a vital strategic frontier for China’s global energy leadership and for driving the commercialization of clean technology. — Mrigakshi Dixit, Interesting Engineering, 29 June 2026

Though the leaders of frontier labs have bridled at the possibility of losing time in the intense global AI race, Commerce Department spokesman Benno Kass cited the speed with which the government acted to address its concerns about Anthropic. — Reed Albergotti, semafor.com, 26 June 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