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

Thailand and Cambodia fought a five-day border conflict in July that killed dozens of people and displaced about 200,000 on both sides of the frontier. —Helen Regan, CNN Money, 13 Nov. 2025

Set on the desolate frontier, Where the Sparrows Fly follows Truman Kersh, a drifting con-man and card-shark, whose latest scam ends in bloodshed. —Andreas Wiseman, Deadline, 12 Nov. 2025

Edie Parker has been at the forefront of this frontier, too, winning over the TikTok masses first with avant-garde accessory innovations like its Burn Bag and bejeweled lighter cases before introducing its Flower subsidiary. —Kaleigh Werner, Footwear News, 11 Nov. 2025

While video generation has grabbed many of the headlines, that realm is painstaking and filled with errors, which is why many experts see AI voices as a much nearer frontier in the push to make media synthetic. —Steven Zeitchik, HollywoodReporter, 11 Nov. 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