| You are perfectly right. The words that are interchangeable (i.e. synonymous) at the individual level are a strict subset of the words that are interchangeable (synonymous) at the population level. In my opinion, when claiming that 2 words are "interchangeable" without any additional details, the expected meaning is that the words are "interchangeable" at the individual level. When they are "interchangeable" at the population level, the expression "interchangeable words" does not seem appropriate, because you cannot interchange just the words, leaving everything else the same. You actually have to interchange 2 humans, who, when speaking about the same thing will use different words, like a British and an American, when speaking about something that is named differently across the ocean. With buffalo and bison, even saying that they were interchangeable at the population-level seems a stretch, because they were never synonymous, even for different people. For some people, "buffalo" meant "any kind of wild ox", while for other people "bison" meant "a specific kind of wild ox from Germany" (while for the latter "buffalo" meant "a specific kind of wild ox from Africa"). So even when considering the entire Roman and Greek population, it is very unlikely that it would have been possible to find 2 people who assigned identical meanings, the first to "bison", and the second to "buffalo". The African buffalo described by Pliny was not the animal named now "African buffalo", which lives in more southern parts of Africa and which was probably unknown to the ancient Greeks and Romans. "Buffalo" is an old Greek word, which was much later borrowed into the Latin language. The word referred initially to some large kind of antelope from Egypt, and this is how the word was still used by Pliny (who e.g. mentioned that the body of a "buffalo" resembles more the body of a stag than the body of an ox). Relatively late in the Greek history, after the expeditions of Alexander the Great, when the Greeks had learned a lot about the Indian animals, plants and minerals, the Greek word "buffalo" began to also be used for the Indian domestic buffalo, hence the modern usage of the word. Many centuries later, after most people no longer had any knowledge about the African antelopes, but were familiar with the domestic buffaloes, the term "wild buffalo" began to be applied to the wild bovids resembling the Indian buffalo, including to the one named now "African buffalo". In the case of the American bison, which is not similar to any kind of buffalo (in the modern sense), the name buffalo was applied by people for whom it had the old meaning of "any kind of wild ox". |