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

Amid social media’s reckoning, however, artificial intelligence chatbots are emerging as the next frontier in the fight to make technology safer for young people. —Barbara Ortutay, Chicago Tribune, 26 Mar. 2026

This week, the Marlins officially enter a new frontier, presenting their games via a mix of streaming and stand-alone channels on five cable and satellite providers. —Barry Jackson, Miami Herald, 26 Mar. 2026

The nod to Star Wars hints at a new frontier, but the Meta site is so disorientingly vast that what’s happening there feels less like sci-fi and more like the early stages of a city rising from the dirt. —Sharon Goldman, Fortune, 26 Mar. 2026

Virtual reality was once touted as the next big frontier for gaming, promising to bring players into immersive worlds. —Gieson Cacho, Mercury News, 26 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