frontier
//frʌnˈtɪər//
Noun
frontierSingular
frontiersPlural
1
A border between two countries or regions; the extreme limit of settled or developed territory
They crossed the frontier between France and Spain.
2
The extreme limit of understanding or achievement in a particular field or area of knowledge
Scientists are pushing the frontiers of medical research.
3
An undeveloped or wild region, especially in the American West during the period of westward expansion
Pioneers traveled west to settle the frontier in the 1800s.