Eponyms is a free and very useful medical reference tool. It lists medical eponyms and their definitions in a clear way. The graphical user interface helps a lot in making this a great app. There are two ways in which you can search for an eponym. First, you can scroll through the list and click on the desired one. Or you can use the search feature at the top of the screen. When you click on an eponym, its definition will be shown on the right pane. By default, the list shows every eponym but you can choose a field of study from a drop-down menu to narrow the results down.
This is a great app to study eponyms, and there are two buttons that help a lot in this regard. They are located in the top-right corner of the screen, and are called Random Title and Random Text. When you click on Random Title, a title will be shown, and the idea is that you define it mentally or in writing. Then you can test your knowledge by clicking the Solve button, which will display the eponym's definition. The second button, Random Text, works similarly, but the title isn't shown; only the definition.
Eponyms comes with over 1700 medical eponyms. I like that you can add eponyms to your bookmarks to group them in a different list.