Iroquoian word Ontarí:io, which is most commonly translated as "great lake" or "beautiful lake," though some sources interpret it as "lake of shining waters" or "sparkling water." 

The name predates both Canada and the United States, appearing on European maps in the mid-17th century (first recorded as Lacus Ontarius in 1660). The Canadian province of Ontario was named after the lake, not the other way around