boundary/ˋbaUndərI; ˈbaʊnd$ri/n [C] plural boundaries 1 the line that marks the edge of an area of land [→ border] 分界线﹔边界: +between The Ohio River forms a natural boundary between Ohio and Kentucky. 俄亥俄河在俄亥俄州和肯塔基州之间形成了一道自然的边界。2 the limit of what is acceptable or thought to be possible 界限﹐限度: +of the boundaries of human knowledge 人类知识的范围