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

Experts also noted that DeepSeek made no reference to using Chinese chips during training, which is a notable omission given the broader push for technological self-sufficiency, and one that stands out as the model continues to lag behind leading US frontier systems. —Bojan Stojkovski, Interesting Engineering, 26 Apr. 2026

But the new frontier in the talent war speaks to AI giants’ changing priorities. —Seema Mody,kate Rooney, CNBC, 25 Apr. 2026

Introduced by Walt Disney in California in 1955, it was designed as a tribute to pioneer spirit, with riverboats, wilderness trails and frontier towns. —Jessica Mekles, FOXNews.com, 25 Apr. 2026

Today’s newsletter takes you on a cruise to see the next frontier of battery deployment. —Fabiano Maisonnave, Bloomberg, 25 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