frontier

UK: /ˈfrʌntɪə^r/, /ˌfrʌnˈtɪə^r/

US: /frʌnˈtɪr/

US: (frun tēr′, fron-; also, esp. Brit., frun′tēr)

WordReference Random House Learner's Dictionary of American English © 2025

fron•tier /frʌnˈtɪr/   n. [countable]

1. the border between two countries:
   the frontier crossing.
2. land that forms the furthest regions of a country or territory.
3. Often, frontiers. the limit of knowledge or the most advanced achievement in a particular field:
   the frontiers of medical research.

adj. [before a noun]

4. of, relating to, or located on a frontier:
   a frontier town.

fron•tiers•man, n. [countable] , pl. -men. 
Synonyms

See boundary.

WordReference Random House Unabridged Dictionary of American English © 2025

fron•tier  (frun tēr′, fron-; also, esp. Brit., frun′tēr), n. 

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. 
   • the limit of knowledge or the most advanced achievement in a particular field:
     the frontiers of physics.
   • an outer limit in a field of endeavor, esp. one in which the opportunities for research and development have not been exploited:
     the frontiers of space exploration.
4. Mathematics boundary (def. 2).

adj. 

5. of, pertaining to, or located on the frontier:
   a frontier town.

• Old French frontier, equivalent. to front (in the sense of opposite side; see front) + -ier -ier²
• Middle English frounter 1350–1400

fron•tier′less, adj. 
fron•tier′like′, adj. 
Synonyms

• 1. See boundary. 

Collins Concise English Dictionary © HarperCollins Publishers::

frontier / ˈfrʌntɪə frʌnˈtɪə/ noun

1. the region of a country bordering on another or a line, barrier, etc, marking such a boundary
2. (as modifier): a frontier post
3. the edge of the settled area of a country
4. (often plural) the limit of knowledge in a particular field: the frontiers of physics have been pushed back

Etymology: 14th Century: from Old French frontiere, from front (in the sense: part which is opposite); see front