| 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.
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| 4. | Mathematics. boundary (def. 2). |
| 5. | of, pertaining to, or located on the frontier: a frontier town. |
| 1. | something that indicates bounds or limits; a limiting or bounding line. |
| 2. | Also called frontier. Mathematics. the collection of all points of a given set having the property that every neighborhood of each point contains points in the set and in the complement of the set. |
| 3. | Cricket. a hit in which the ball reaches or crosses the boundary line of the field on one or more bounces, counting four runs for the batsman. Compare six (def. 5). |
"What is the frontier? ... In the census reports it is treated as the margin of that settlement which has a density of two or more to the square mile." [F.J. Turner, "The Frontier in American History"]Frontiersman is from 1782.