In many languages, the morphemes which enter into a single word vary in their phonemic representation depending on the other morphemes present in the same word; at the same time, the shapes of whole words vary depending on their position relative to each other and on the shapes of adjacent words. The most convenient way to describe the alternations involved is in terms of ‘internal’ and ‘external sandhi’; the term ‘sandhi’ [...] was used for just these phenomena by the ancient Hindu grammarians.
- Hockett (1958), a pag.277