That which limits the extent of something; a limit, an end point, a boundary. Usually in plural. Now rare or archaic.

singular and plural. The part of a country which fronts or faces another country; the marches; the border or extremity conterminous with that of…

The edge, verge, or rim of something; the border of a country. Obsolete.

A boundary, a border; a limit. Obsolete.

gen. A fence or material obstruction of any kind erected (or serving) to bar the advance of persons… A fortified frontier; a frontier generally; spec.…

The strip of land along the border between two countries or districts; a frontier-line; often figurative, the boundary between areas, classes, etc.