Q From Peter Smith: If a mountainside is the side of a mountain, the seaside is beside the sea and a riverside is beside a river, what is the countryside beside?
A Originally it referred to an element of open landscape. Since flatness is rare in the country, most of it can be thought of as being on one side or the other of some natural feature, such as a hill or a valley. So the term originally meant a rural feature that had a natural unity and was on one side of such a feature. This fits with the older sense of country as being some tract of land that had well-defined limits or boundaries. In the nineteenth century, countryside became fashionable among descriptive writers following the Wordsworthian discovery of the aesthetic value of landscape, and its sense shifted to mean not one part or section of the visible terrain, but the natural or rural landscape as a whole.