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

For the British Crown, such frontiers were smudges on the edge of the map. —Daniel Immerwahr, New Yorker, 4 May 2026

The frontiers of materials science, sensing, and engineering offer hope for faster, cheaper, less energy-intensive solutions to this grand challenge. —Alaina Harkness, Chicago Tribune, 3 May 2026

Whilst the Yangtze River Delta has become the nexus of full-stack, frontier generative AI models, Shenzhen is racing ahead as the powerhouse of China’s embodied AI and hardware efforts. —Brian Wong, Fortune, 3 May 2026

The analysts predict that each of the frontier Chinese AI models can achieve at least $1 billion in revenue this year, and more than double that next year. —Evelyn Cheng, CNBC, 3 May 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