[{"Bold_text": "noun", "List Items": ["the part of a country that borders another country; boundary; border.", "the land or territory that forms the furthest extent of a country's or inhabited regions.", "Oftenfrontiers.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.", "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.", "Mathematics. boundary(def3) boundary(def3)."]}, {"Bold_text": "adjective", "List Items": ["of, relating to, or located on the frontier:a frontier town."]}]