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

Still, he was eager to explore a fresh frontier.

From Los Angeles Times • Apr. 1, 2026

“We continue to believe it is highly unlikely that tools from the frontier labs will displace cybersecurity vendors, particularly those that primarily provide solutions that do real-time detection & response,” D.A.

From MarketWatch • Mar. 27, 2026

Cooke’s agents sold in small towns, frontier settlements, and mining camps.

From Barron's • Mar. 25, 2026

Many of these requirements are impractical for frontier AI development.

From The Wall Street Journal • Mar. 23, 2026

The White brothers were part of a small contingent of frontier lawmen who were known inside the bureau as the Cowboys.

From "Killers of the Flower Moon" by David Grann