Ksiądz (priest) – książę/księżniczka (prince, princess) –księżyc (Moon)- książka (book).
Why all of these words with completely different meaning looks so similar in Polish?
Ksiądz (current meaning priest) in old Polish meant ruler/warlord. His son – successor was referred to as książę (similar as current meaning- a member of the royal family) or księżyc (current meaning Moon).With time after Christianity spread on Polish lands word ksiądz changed meaning for the priest and księżyc gained figurative expression as a satellite of Earth= Moon.
All of these words have the same root as książka (book) – it can easily be explained by the fact that in the Middle Ages priests and rulers were fairly the only ones who had the ability to write and read. Because of that in Polish word księżniczka describing female sovereign or monarch looks so much different than in other languages 🙂