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

Beijing removed Ma as Xinjiang’s party secretary in July, installing a senior ethnic-affairs official to lead the Central Asian frontier region where about 12 million Turkic-speaking Muslim Uyghurs live.

From The Wall Street Journal • Apr. 3, 2026

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

Causey was a master of half expression, half smiles, and half glowers, for all nuances of expression stopped at the invisible frontier that marked the dead sector of his face.

From "The Great Santini" by Pat Conroy