Each week , we tell about terms and expressions we use in American English . Sometimes we give you the origin , or starting point . But oftentimes language experts do not know exactly how a word or expression came to be . So , there can be many “origin ” stories . Today we run into just that problem . But it is not about a word or expression , but rather a symbol – Rx . A symbol is a sign that represents one or more words . The “Rx ” sign is formed by placing a line across the right foot of the letter “R .” It represents the word “prescription ” and has come to mean “take this medicine .” It also appears on bottles of pills and other medicines . But how did Rx come to mean prescription medicine ? One common explanation is that “Rx ” has Latin roots . Some word historians suggest that “Rx ” gets its meaning from the Latin word “recipere ,” meaning “to take .” They add that by the late 1500s , the spelling of the word and its meaning had changed . It became “recipe ,” meaning a “medical prescription .” This meaning remained in use until the middle of the 1700s . At that time , people also began to use the word “recipe ” in food preparation , as we do today . Yet , the symbol “Rx ” and the meaning “take this medicine ” stayed unchanged . Okay , so that origin story is not so interesting . Instead , let's hear another story that also claims to explain the history of Rx . Some experts say the sign began 5,000 years ago in Egypt . At that time , people prayed to Horus , the god of the Sun . Legend says that when Horus was a child , Seth , the demon of evil , attacked him . When Seth put out the eye of the young Horus , the mother of Horus called for help . Thoth , the god of learning and magic , answered her cries . With his wisdom and special powers , Thoth healed the eye of Horus and the child was able to see again . The ancient Egyptians used a picture of the eye of Horus as a magic sign to protect themselves from disease , suffering and evil . Long after the collapse of ancient Egypt , doctors and scientists in Europe continued to use the sign . But over the years , it changed from the eye of Horus to the sign for Jupiter , the chief god of the Romans . Jupiter's sign looked much like the printed number “four .” Over time , that sign also changed . It became the easily-recognized letter “R ” with a line across its foot . The sign no longer means help for the sick from an ancient god , but rather “medicine to take .” So , that is what the symbol means even though we cannot guarantee how it came to be . To make it up to you , we give you a useful , medicine-related expression . Now , when a doctor prescribes a patient medicine , it is only for that patient , no one else . Giving someone a taste of their own medicine sounds like the right thing to do . A person is supposed to take the medicine a doctor has prescribed for them . But that is not what this expression means . When you give someone a taste of their own medicine , you treat them as they have treated you . And we almost always use this expression when talking about bad treatment . Let's hear how it can be used . Great party , Chuck ! Hey , can you keep an eye on things here ? I need to go and get Natalie . I thought Michael was giving her a ride . That's what he said . But he hasn't shown up . She's been waiting at her place for an hour . Michael has been doing that a lot lately . He promises to do something and then doesn't follow up . Last week , we were supposed to go to the movies , but he stood me up . And he didn't even call to let me know he couldn't make it . He was a no-show for me just last week too . You know , one day , we should give him a taste of his own medicine . We should agree to do something -- something really important to him -- and then never show up . Having a taste of his medicine might help . But you know we'll never do that . Look , you stay here and take care of the party . I'll go and get Natalie . That would be a big help . Be careful on the road . Do you use medicine in a similar expression in your language ? Or simply tell us about a time when you had to give someone a taste of their own medicine .