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; front ) + -ier -ier ²

Example Sentences

“The work of defending the world’s cyber infrastructure might take years; frontier AI capabilities are likely to advance substantially over just the next few months,” Anthropic says.

From The Wall Street Journal • Apr. 8, 2026

"This paper represents a critical leap into a much larger, more exciting frontier."

From Science Daily • Apr. 7, 2026

Dog poo bags are not the only indignity the famous defensive frontier has to endure.

From BBC • Apr. 6, 2026

At the time, however, the frontier – with its rugged cowboys, miners and railroad men – defined American manhood.

From Salon • Apr. 6, 2026

To understand the answer to this paradox, we have to remember that, until 400 B.C., the frontier of Tsushima Strait separated not rich farmers from poor hunter-gatherers but poor farmers from rich hunter-gatherers.

From "Guns, Germs, and Steel: The Fates of Human Societies" by Jared M. Diamond