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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Synonym Usage

See boundary.

Other Word Forms

Derived Forms

• semifrontier
  noun
• frontierless
  adjective
• transfrontier
  adjective
• frontierlike
  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

In that environment, the helmets may have been intended for local militias, forces serving the Kingdom of Valencia, or armed groups responsible for defending the region's maritime frontier.

From Science Daily • Jun. 8, 2026

The SpaceX IPO is the biggest sale of its type in history but it's just the first of a slew of mega-sales of shares in the companies at the frontier of the AI economy.

From BBC • Jun. 8, 2026

If EVs are coming for the world, this is the rough-and-tumble frontier.

From Barron's • Jun. 8, 2026

He and Erkılıç have achieved international acclaim for their team’s decades of foundational experimentation collaborating with dataset intelligences at the AI frontier, as well as for architecturally-scaled, narratively engaged visual embodiments of abstract technological constructs.

From Los Angeles Times • Jun. 5, 2026

And all that time the womenfolks and children of Salt Licks would be left in a wild frontier settlement to make out the best they could.

From "Old Yeller" by Fred Gipson