Sound is an interesting word because, despite its relative simplicity, it carries a number of extremely divergent meanings. As is often the case with English homonyms, this is due to words entering the language from other languages with which it came into contact. In the case of sound, this would be Norman French and Old Norse.
When considering sound in a modern context, three potential meanings quickly come to mind. The first, and native English, meaning is to be whole or healthy. The word is still used in this context relatively often (e.g., in phrases like of sound mind) and in phrases relating to inanimate objects (e.g., determining that a set of stairs is sound.). As might be expected, there are strong cognates in German (gesund, Gesundheit) and Dutch (gezond, gezondheid).
The second meaning that comes to mind easily is something that is heard. This meaning came into English via French (son), itself derived from the Latin sonus, which both carry this meaning. The word morphed in Middle English into soun and from there seems to have been modified further into a more familiar form by adding a ‘d’. In this case the equivalent terms in German and Dutch (klingen and klink, respectively) do still have a cognate in English, which is clink. Clink, however, also seems to have been borrowed from Dutch and refers in English to a specific type of sound and not sound in general.
The third meaning of sound that comes to mind immediately is of a narrow body of water, either between two landmasses or between an island and the mainland. Two well known examples from the United States are Puget Sound and Long Island Sound. This meaning comes from the Old Norse word sund, which was used to describe just such a body of water. The same word also exists in Old English, but seems to be indirectly related, as it holds a meaning related to swimming. As with the Latin-derived term described above, there seems to have been an effort to make the word conform to comfortable patterns by changing the spelling and pronunciation, in this case by adding a vowel.
English is perhaps uniquely susceptible to these types of overlaps and inconsistencies due to the amount of borrowing that has gone on from other languages over the centuries. However, the issue has been exacerbated by the fact that, unlike other languages such as French, German and Afrikaans to name a few, there is no board or commission designated to oversee the language and institute rational reform or even consistency within the language.
As a native English speaker, I recall being baffled as a child at English spelling conventions such as pronouncing “laugh” as “laf” and I have always marvelled at the ability of people around the world to learn what to me seems to be a largely non-sensical and capriciously structured language. Having spent a considerable amount of time studying other languages, I find that it is hugely helpful to have reliable rules and phonetic spelling applied to a language and I believe English could benefit greatly from this.