[fron.tier] n [ME fronter, fr. MF frontiere, fr. front] (15c) 1 a: a border between two countries b obs: a stronghold on a frontier
2. a: a region that forms the margin of settled or developed territory b: the farthermost limits of knowledge or achievement in a particular subject c: a line of division between different or opposed things "the ~s separating science and the humanities --R. W. Clark" d: a new field for exploitative or developmental activity -- frontier adj