A pachyderm is any of several large mammals with very thick skin, including elephants, rhinoceroses, and hippopotamuses. The word comes from Greek roots meaning “thick skin,” which perfectly describes these massive animals.

An elephant's skin can be over an inch thick in places, tough enough to protect against thorns, insect bites, and the blazing sun. A rhinoceros has skin like armor plating. Even though we now know that elephants, rhinos, and hippos aren't as closely related to each other as scientists once thought, the word pachyderm remains useful for describing these thick-skinned giants.

You might hear someone jokingly call a person a pachyderm if they seem thick-skinned in an emotional sense, meaning insults and criticism don't bother them. If your friend stays cheerful even when others tease him, you could say he has pachyderm-like resilience. The word captures both physical toughness and the ability to brush off things that might hurt someone more sensitive.