K?esomysl was the fifth of the seven Bohemian mythical princes between the (also mythical) founder of the P?emyslid dynasty P?emysl the Ploughman and the first historical prince Bo?ivoj. The names of the princes were first recorded in Cosmas chronicle and then transmitted into most of the historical books of the 19th century including Franti?ek Palacký's The History of the Czech Nation in Bohemia and Moravia.
One theory about the number of the princes is propped on the frescoes on the walls of the Rotunda in Znojmo, Moravia but Ane?ka Merhautová claimed that the frescoes depict all the members of the P?emyslid dynasty including the Moravian junior princes.
K?esomysl's name is thought to be derived from the old Slavonic words "k?esat" meaning to strike a light and "mysl" meaning mind or spirit thus literally the name should have meant "lighting the mind". The suffix -mysl is also in the other mythical names P?emysl and Nezamysl. Závi? Kalandra thought the names of the seven princes were cryptic names of ancient Slavonic days of the week - K?esomysl being the fifth - Thursday, in Latin Iovis Dies whereas Jupiter and Thor were both gods of thunder the word "k?esat" is explained here as to strike the lightnings. Another theory says that the names were mistaken from a coherent and partly interrupted old Slavonic text.