the frontierSGan area where people have never lived before, that not much is known about, especially in the western US before the 20th century 〔尤指20世纪前美国西部的〕边远地区，荒野地区；边疆 a novel about a family’s struggle on the American frontier 描写一家人在美国边远地区奋斗的小说
space, the final frontier 太空，最后的边界
the frontier• Alaska is known as the last frontier.• Wilder's novel is about a family's struggle on the American frontier.
→ the frontier at frontier(1)