Definition of frontiers:
(n) :
The part of a country which borders or faces another country or unsettled region.
(n) :
The most advanced or recent version of something; the leading edge.
(v) :
(intransitive) To live as pioneers on frontier territory.
(n) :
(obsolete) An outwork of a fortification.
(v) :
(transitive, obsolete) To place on the frontier.
(n) :
A city in North Dakota.