1 [C] the frontier (between A and B) the line where one country joins another; border 国界;边界:
the end of frontier controls in Europe.欧洲国家之间不再有边境检查☞Look at the note at border. 参看border的注释。
2the frontiers [pl] the limit between what we do and do not know 知识的极限:
Scientific research is constantly pushing back the frontiers of our knowledge about the world.科学研究不断扩大我们对这个世界的认识。