frontier

frontier — noun

1. The official boundary marking where one country ends and another begins, usually

1.nounB1
Definition

The official boundary marking where one country ends and another begins, usually with checkpoints where travellers must show identification documents.

Example

The train crossed the frontier between France and Italy just before noon.

crossed the frontier between [country] and [country]

Gabriel had to show his passport at the frontier checkpoint before entering Poland.

at the frontier checkpoint

Common collocations
  • cross a frontier
  • at the frontier
  • along the frontier
  • frontier crossing
  • frontier checkpoint
  • frontier between
Synonyms
  • border

    general term for any dividing line between areas; in American English 'border' replaces 'frontier' for country-to-country boundaries

  • boundary

    more formal and can apply to any kind of limit, not just between nations

  • line

    informal; a neutral word for any demarcation

Grammar Patterns

the frontier

frontier between [country] and [country]

Usage Note

In British English 'frontier' is the everyday word for a national border with passport checks. In American English 'border' is far more common for this meaning; 'frontier' in US contexts usually refers to Sense 2 below.

Common Mistakes

They built a wall along the frontier of the garden.
They built a wall along the boundary of the garden.
'frontier' refers to a border between countries, not the edge of a private property.
The river forms the natural frontier of the park.
The river forms the natural boundary of the park.
use 'boundary' for non-political dividing lines.

2. The outer edge of a region where people have built homes and communities, beyond

2.nounB2
Definition

The outer edge of a region where people have built homes and communities, beyond which the land remains wild and largely unexplored, especially referring to the western United States during the 1800s.

Example

The Gabriel family traveled west to start a new life on the American frontier.

on the [American] frontier [historical]

Life on the frontier required settlers to build their homes and grow all their food.

Common collocations
  • the American frontier
  • on the frontier
  • frontier life
  • frontier town
  • frontier settlement
  • pioneers on the frontier
Synonyms
  • borderland

    the land near a boundary; less specific to settlement patterns

  • wilderness

    emphasizes the untamed natural state rather than the settlement edge

  • outskirts

    the outer parts of a town or city, not a historical region

Grammar Patterns

the frontier, on the frontier, the American frontier

Usage Note

This sense is deeply tied to US expansion history. It is often capitalized ('the American Frontier') when treated as a specific historical period or region. The word also appears in similar contexts for other countries (e.g., 'the Brazilian frontier').

Common Mistakes

My neighbor built a fence on the frontier of his yard.
My neighbor built a fence on the edge of his yard.
'frontier' in this sense refers to a large historical region, not a backyard boundary.

3. An imagined boundary that marks where one idea, quality, or condition ends and a

3.nounB2
Definition

An imagined boundary that marks where one idea, quality, or condition ends and another begins.

Example

The frontier between art and entertainment is not always easy to draw.

the frontier between [X] and [Y] [abstract]

Minh argued that the frontier between public and private life has become increasingly blurred.

Common collocations
  • frontier between
  • blur the frontier
  • draw a frontier
  • the frontier separating
Synonyms
  • dividing line

    more direct and less metaphorical; common in everyday speech

  • boundary

    can be physical or abstract; more general than 'frontier'

  • threshold

    emphasizes the point at which one state crosses into another

Grammar Patterns

the frontier between [X] and [Y]

Usage Note

This sense is almost always followed by 'between' with two contrasting nouns. The frontier is not a fixed line — it is a matter of interpretation or debate.

Common Mistakes

The frontier of rich and poor is growing wider.
The gap between rich and poor is growing wider.
use 'frontier between X and Y,' not 'frontier of X and Y.'

4. The most advanced or extreme point reached in a field of learning, discovery, or

4.nounC1
Definition

The most advanced or extreme point reached in a field of learning, discovery, or achievement, beyond which new work remains to be done.

Example

Researchers at the institute are pushing back the frontiers of medical science.

pushing back the frontiers of [field]

Hyun believes space exploration represents humanity's next great frontier.

next frontier [metaphorical]

Common collocations
  • frontiers of science
  • push back the frontiers
  • new frontier
  • expand the frontiers
  • last frontier
  • frontiers of knowledge
Synonyms
  • cutting edge

    emphasizes the newest, most advanced developments; more informal and technology-focused

  • forefront

    the leading position in a field; suggests active leadership rather than the boundary of knowledge

  • vanguard

    the group leading a movement or innovation; person-focused rather than field-focused

Grammar Patterns

the frontiers of [field], push back the frontiers, new frontier

Usage Note

Often used in the plural ('frontiers') to suggest many directions of progress. The phrase 'new frontier' is a common fixed expression for any exciting, unexplored area of activity.

Common Mistakes

She is at the frontier of her career.
She is at the forefront of her field.
'frontier' refers to the limits of a whole field, not an individual's career stage.
The frontier of the city is expanding.
The outskirts of the city are expanding.
use 'frontier' for knowledge/achievement limits, not for urban growth.

Word family

  • frontiersman
    nounC1
  • frontierswoman
    nounC2
  • frontierless
    adjectiveC2

Synonym discussion

Sense: noun/1

'Border' is the most common everyday word for the line separating two countries or regions; you use it at a 'border crossing' and talk about 'crossing the border.' 'Boundary' is more formal and can apply to anything from a property line to a national limit — it is broader and less tied to travel or control. 'Frontier' (Sense 1) overlaps with 'border' but is more common in British English for national boundaries; in American English 'frontier' in this sense sounds slightly formal or historical. For example, a British speaker might say 'the French frontier,' whereas an American would say 'the French border.' The choice depends on variety: use 'border' for everyday international limits and 'frontier' when the context is British, historical, or deliberately formal.

border ↗boundary ↗frontier ↗

Common collocations

Nouns

Phrases

  • cross the frontier
  • push back the frontiers
  • new frontier
  • last frontier
  • frontier between
  • frontier of

Prepositions

Etymology

LatinOld FrenchEnglish

From Old French 'frontiere' (borderland, frontier), from 'front' (forehead, front). The Latin root 'frons' meant 'forehead' or 'front,' and the sense shifted to 'the part of a country that faces another' — the front line of a territory. The word entered English in the 1400s, first referring to a military front or border fortification. By the 1600s it was used for the settled edge of a country. The metaphorical meaning — the limit of knowledge or achievement — emerged in the late 1800s and became especially common in science and technology contexts in the 1900s.