frontier

American  

[fruhn-teer, fron-, fruhn-teer] / frʌnˈtɪər, frɒn-, ˈfrʌn tɪər /

noun

1. the part of a country that borders another country; boundary; border.

2. the land or territory that forms the furthest extent of a country's settled or inhabited regions.

3. Often frontiers.

   1. the limit of knowledge or the most advanced achievement in a particular field.

      the frontiers of physics.

   2. an outer limit in a field of endeavor, especially one in which the opportunities for research and development have not been exploited.

      the frontiers of space exploration.

4. Mathematics. boundary.

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adjective

1. of, relating to, or located on the frontier.

   a frontier town.

frontier British  

/ frʌnˈtɪə, ˈfrʌntɪə /

noun

1. 1. the region of a country bordering on another or a line, barrier, etc, marking such a boundary

   2. ( as modifier )

      a frontier post

2. 1. the edge of the settled area of a country

   2. ( as modifier )

      the frontier spirit

3. (often plural) the limit of knowledge in a particular field

   the frontiers of physics have been pushed back

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Related Words

See boundary.

Other Word Forms

• frontierless adjective
• frontierlike adjective
• semifrontier noun
• transfrontier adjective

Etymology

Origin of frontier

1350–1400; Middle English frounter < Old French frontier, equivalent to front (in the sense of opposite side; see front) + -ier -ier ²

Explanation

A frontier represents uncharted territory. It could be a remote piece of land or a new field of study, but if someone calls it "the frontier," you are challenged to explore it. The noun frontier has several meanings. It can refer to the wilderness at the edge of a settled area (picture covered wagons pushing westward) or it can mean a field of study that has not yet been explored (picture genetically engineering pet dinosaurs). Deriving from "the front line of an army," a frontier can be thought of as an offensive line in a battle — always pushing forward, trying to conquer new territory.

Example Sentences

The hunt for extraterrestrial life is entering a new frontier, writes science journalist Nadia Drake.

From The Wall Street Journal • Apr. 24, 2026

Its daily work is to identify national security risks in those transactions, which involve high-profile, frontier technologies like robotics, autonomous systems, and biotechnology.

From Barron's • Apr. 22, 2026

All the most powerful and advanced AI models - known as frontier AI - are developed outside of the UK, with the top-tier companies based in the US or China.

From BBC • Apr. 21, 2026

“In the medium to longer term, there will be a risk premium attached to every barrel coming out of the Persian Gulf that will push people into frontier exploration.”

From The Wall Street Journal • Apr. 20, 2026

Truth was, he knew that the tribe of old frontier lawmen to which he belonged was vanishing.

From "Killers of the Flower Moon" by David Grann