Is it ensure, insure, or assure?
a fabled marine creature with the head and upper body of a human being and the tail of a fish. Similar divine or semidivine beings appear in ancient mythologies (e.g., the Chaldean sea god Ea, or Oannes). In European folklore, mermaids (sometimes called sirens) and mermen were natural beings who, like fairies, had magical and prophetic powers. They loved music and often sang. Though very long-lived, they were mortal and had no souls