On this weekly program , we explore the origin and usage of common expressions in American English . For example , sometimes when Americans do not understand something they say , ‘It's all Greek to me .” This saying does not make sense , of course , if you actually speak Greek . But today , we are going to talk about a Greek word and what it means in American English . “Eureka !” is Greek for “I have found it !” It is something we say when we have figured out a solution to a complex problem . “Eureka ” is a kind of interjection . Interjections are the quick , short words or sounds we cry out when we are feeling intense emotion . They can express pain , surprise , anger or joy . These kinds of words also are called exclamations . Someone cries “Eureka ” to express excitement when that person makes a discovery . The story behind “Eureka ,” however , is somewhat of a guess . Some say it goes all the way back to the time of ancient Greece and an inventor named Archimedes (c . The king of Syracuse , Heiro II , gave Archimedes a difficult problem to solve . The king wanted to know if goldsmiths had used pure gold to make his crown . This problem troubled Archimedes . How could he learn if the crown was pure gold ? One day , he stepped into the water of a bathtub . He saw that the water flowed over the top of the tub . The water that overflowed was displaced by his body . When Archimedes climbed in and out of the bath , he carefully studied the displaced water . He noticed that the more his body sank into the water , the more water was displaced . This meant that the displaced water measured his volume exactly . Suddenly , Archimedes realized how he could test the gold in the king's crown . He knew that gold is heavier than silver . So , he reasoned that a crown mixed with silver would have to be bulkier than one made only of gold if both weighed the same . Therefore , it would displace more water than a crown of pure gold . Eureka !” meaning , “I have found it ! I have found it !” In another version of the story , the king gives a different puzzle to Archimedes to solve . Archimedes must figure out how to build a massive ship that won't sink . Again , he supposedly makes his discovery in a public bath . Both are great stories , but most likely , Archimedes never said “Eureka !” What we do know is that Archimedes discovered the law or buoyancy , or what engineers still call today , the Archimedes principle . But let's go back to “eureka ” as an expression . “Eureka !” has another historic connection to gold . This time it happened during more modern times in the United States . During the California gold rush , prospectors looking for gold in the Californian hills were said to yell “Eureka ! I found it !” when they struck gold . To this day , California's state motto is Eureka ! The word “Eureka !” also lives on in scientific communities . The American Association for the Advancement of Science calls its breaking scientific news site EurekAlert . However , these days , saying “Eureka !” as a way of expressing an amazing discovery is out of style . One interjection that has replaced “eureka ” is “a-ha !” But both “eureka moments ” and “a-ha moments ” are used to describe the times we are experiencing a breakthrough discovery . Albert Einstein arriving at his theory of relativity and Isaak Newton getting hit on the head with an apple are both examples of eureka moments . Here is how to use it in everyday conversation . If your classmate or work colleague seems to be about to discover something big and important , others might warn you to stay away . “Don't bother her . She's having a Eureka moment ." When a character in comics or in an animated film has a really great idea , sometimes a lightbulb appears above their head . So , saying “lightbulb ” is a funny way of saying , “I just had a brilliant idea !”