An interjection is a word or cry that expresses sudden or strong feeling. The interjection "eureka" comes from the Greek word "heureka," which means "I have found it." According to legend, the Greek inventor Archimedes found he was able to determine the purity of gold by a principle based on the amount of water that spilled out of his bathtub when he stepped into it. He was so excited by this discovery that he yelled out "Heureka!" and supposedly ran from his bath out into the streets of Syracuse. "Eureka" has since become a traditional response to a sudden discovery or flash of inspiration.