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 French company’s announcement follows on from model releases from the likes of DeepSeek and Google in recent weeks, as AI labs across the globe scramble to remain at the frontier of research while also building out commercial operations. —Kai Nicol-Schwarz, CNBC, 2 Dec. 2025

One clock, representing the infrastructure build-out, is spinning quickly as innovation shifts the frontier of hardware and AI models every six to 12 months, compressing the payback window. —Ravi Kumar S, MSNBC Newsweek, 2 Dec. 2025

The coming era of AI agents promises revolutionary efficiency, but also a new frontier of cybersecurity risk. —Bojan Stojkovski, Interesting Engineering, 1 Dec. 2025

This tension between efficiency and inspiration now defines retail’s next frontier. —Cecile Van Steenberge, Fortune, 28 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