Zichmni is the name of an explorer-prince who appears in a 1558 book by Nicolò Zeno of Venice, allegedly based on letters and a map dating to the year 1400 by the author's ancestors, brothers Nicolò and Antonio Zeno. Zichmni is described as a great lord of some islands off the southern coast of Frislanda, a possibly fictitious island claimed to be larger than Ireland and located south of Iceland.
According to the book, the letters provided a first-hand account of a voyage of exploration undertaken in 1398 by Prince Zichmni, accompanied by the Zeno brothers. The book claims that the voyagers crossed the North Atlantic to Greenland. A few recent authors speculate that they may have reached the coast of North America. Historians consider either the 1558 book or the letters on which it is based to be a hoax.
Some proponents of the authenticity of the tale maintain that Zichmni was a Scottish nobleman named Henry Sinclair. However, scholars point to many flaws in this identification and consider it extremely unlikely.