Final answer:
The term humor originally referred to the four basic substances that composed the universe: earth, air, fire, and water, as believed by ancient Greek philosophers. However, this understanding has been replaced by modern scientific knowledge.
Step-by-step explanation:
The term humor originally referred to one of the four basic substances that composed the universe: earth, air, fire, and water. This concept was introduced by ancient Greek philosophers such as Empedocles, who believed that these four elements were the building blocks of all matter. However, it is important to note that this understanding of humor as the elements has been replaced by modern scientific knowledge.