Kaja is a diminutive of Karolina, itself a Czech variant of Caroline. Caroline originates in Germanic languages and means "free woman". It is a feminine form of Carolus, ultimately derived from Charles. Caroline has been one of the most popular feminine given names over centuries and in various spelling in different countries around the world. It was a popular name within royalty, including several queens of Great Britain. Caroline was also the name of Napoleon Bonaparte's younger sister. Carolina is the name of two U.S. states, North and South Carolina.