Lady of the Lake, the name given to Vivien, the mistress of Merlin, who dwelt in an imaginary lake, surrounded by a court of knights and damsels; also to Helen Douglas, a heroine of Scott's, who lived with her father near Loch Katrine.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Lady of Shalott * La Fayette, Madame de