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

Hark back, for instance, to Austin’s miserable decades as a frontier outpost with few creature comforts before the Civil War. —Michael Barnes, Austin American Statesman, 20 Mar. 2026

YouTube has cemented itself as the new frontier of the podcasting medium, presenting incredible opportunities for reach and audience connection. —Cat Cardenas, Variety, 19 Mar. 2026

Today’s frontier models exceed two trillion parameters and the next generation will be over five trillion. —Sha Rabii, Fortune, 19 Mar. 2026

Heidi is the empowered frontier woman, setting off from her parents’ Colorado lodge to reinvent everything about herself out west with a wild man. —Literary Hub, 18 Mar. 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