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

Hungarians living near the southern frontier, where Orbán made a show of building a border fence during the refugee crisis, are travelling to Croatia to buy cheap groceries. —Kapil Komireddi, New Yorker, 10 Apr. 2026

Already, Israeli strikes near Iran’s eastern frontier are fomenting instability in Pakistan’s restive province of Balochistan. —Charlie Campbell, Time, 9 Apr. 2026

Caracas Bakery, the Venezuelan bakery that started in Doral and then spread to Miami’s MiMo neighborhood and Coral Gables, has a new frontier to conquer. —Connie Ogle april 8, Miami Herald, 8 Apr. 2026

Space enthusiasts often pitch our future in outer space as an inevitability — the result of an innate human drive to explore and pursue new frontiers. —Jackie Wattles, CNN Money, 8 Apr. 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