pachyderm

Once upon a time, if a naturalist wanted to speak about huge animals with very thick skin, they might have called them pachyderms. The word comes from Greek and literally points to the idea of "thick skin." In older writing, it is most often used for elephants and rhinoceroses, and sometimes for hippopotamuses as well. It carries the feeling of an earlier age of nature writing, when people often grouped animals by what they looked like rather than by how they were related.

As science advanced, that way of grouping animals fell out of use. These animals are not all close relatives in the modern scientific sense, so the term is no longer a formal classification. Today, biology focuses more on evolutionary relationships than on visible features such as thick skin. Even so, the word still paints a strong picture of a massive land animal with weight, power, and presence.

You might come across pachyderm in older books or in vivid prose, where a writer wants a grand, slightly old-world word for one of these animals. It is also sometimes used in a figurative way for a person who seems thick-skinned or not easily hurt by criticism, though that use is less common. In modern English, the word survives mostly for its color and style. It is not the everyday scientific name, but it remains a memorable way to call up the image of an elephant, a rhinoceros, or another huge, thick-skinned beast.