Rikke is a diminutive of Frederikke, itself a Danish variant of Frederica. Frederica originates in Germanic languages and means "calm monarch". It is a feminine form of Frederick. Frederica is quite a popular name within royalty. It is also the name of Georgette Heyer's romance novel, as well as the name of several places in the United States. As a feminine given name it is very rare in the U.S.