Isn't Evolution Just a Theory?

Evolution is often criticized by opponents as being "just a theory." This argument is especially common in America, where the word "theory" usually means an unproven idea. However, in science a theory is the highest degree of certainty. Gravity is "just a theory." The Earth orbiting the Sun is "just a theory." By definition, a scientific theory is a hypothesis which has withstood rigorous testing and is well-supported by the facts. There is overwhelming evidence for biological evolution, just as there is overwhelming evidence for gravity.