frontier

/ˈfrʌntɪə(r)/ (bre, ipa) · /frʌnˈtɪr/ (ame, ipa) · /ˌfrən-ˈtir ˈfrən-ˌtir, frän-ˈtir, ˈfrän-ˌtir/ (ame, mw)

frontier — noun

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

1.名詞B1
釋義

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

例句

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

同義詞
  • 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

文法句型

the frontier

frontier between [country] and [country]

用法筆記

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.

常見錯誤

❌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.名詞B2
釋義

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.

例句

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.

同義詞
  • 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

文法句型

the frontier, on the frontier, the American frontier

用法筆記

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').

常見錯誤

❌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.名詞B2
釋義

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

例句

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.

同義詞
  • 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

文法句型

the frontier between [X] and [Y]

用法筆記

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.

常見錯誤

❌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.名詞C1
釋義

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

例句

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]

同義詞
  • 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

文法句型

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

用法筆記

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.

常見錯誤

❌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.