The story
From the name of an area in southern China mentioned by Marco Polo (as Anin, Ania or Anian depending on the text copy), later put by cartographers into area between Asia and America. Before or after the Anian Strait was (probably falsely) reported found by L. Maldonado, the Anian-name was moved by the cartographers to the eastern side of this strait, becoming a location in America (together with Bergi and Tholm, also from Marco Polo, and sometimes also Arsarot, derived from Arzareth found on old maps of northern China).
Etymology from Wiktionary, CC BY-SA 4.0.