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

were sent on 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

• 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

Robotics pioneer Rodney Brooks, former head of the MIT Artificial Intelligence Lab and a founder of iRobot, knows from decades of building real-world applications from frontier technologies, that to be widely adopted, even the most clever tools must leave room for humans. —Gabriel Snyder, MSNBC Newsweek, 25 June 2025

Retirement, commonly referred to as the golden years, is the final frontier. —Oc Register, 22 June 2025

This shift has opened the door to a new kind of security frontier that involves protecting not just human employees, but AI agents acting autonomously across sensitive systems. —Alexander Puutio, Forbes.com, 18 June 2025

The test proposed here advances a new frontier: accepting game rules expressed in a natural language such as English. —Vinay K. Chaudhri, Scientific American, 16 June 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