The name "essential oil" comes from theories in the Middle Ages of a fifth element. People than believed that there were four basic elements that everything was made of: fire, water, air and earth. The elusive "soul" of things was called the quintessential element or the fifth element. Over time, "quintessential" was shortened to "essential". Alchemists said that this element could change iron to gold. Some believed it held the planets in their orbits.