- the part of a country that borders another country; boundary; border.
- the land or territory that forms the furthest extent of a country's settled or inhabited regions.
- 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, especially one in which the opportunities for research and development have not been exploited: the frontiers of space exploration.
- boundary (def. 3).
- of, relating to, or located on the frontier: a frontier town.
- the region of a country bordering on another or a line, barrier, etc, marking such a boundary
- (as modifier)
- US and Canadian
- the edge of the settled area of a country
- (as modifier)
- the limit of knowledge in a particular field
