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
• borderland
• march

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

But now the former astronaut, NFL player, engineer and educator is stepping into yet another new frontier as an author. —Lizz Schumer, People.com, 23 Jan. 2025

By being able to compare these planetesimal belts around other stars with our own Edgeworth–Kuiper Belt, which is a frontier currently being explored by pioneers such as the New Horizons mission, astronomers can uncover the secrets that these frozen realms have kept hidden. —Keith Cooper, Space.com, 23 Jan. 2025

The researchers evaluated several multimodal frontier models, including Anthropic’s Claude Sonnet-3.5, Google’s Gemini 1.5 Pro, and both OpenAI’s GPT-4o and new reasoning model, o1. —Britney Nguyen, Quartz, 23 Jan. 2025

As content moderation efforts are rolled back at Meta (impacting both Facebook and Instagram) and X continues its confused crusade (check out Musk fumbling this recent PR mess with the gamer contingent), TikTok represents a kind of final frontier for contemporary political discourse. —Alison Foreman, IndieWire, 19 Jan. 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

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