It is hardy to identify a lily once the name is lost because there are many that look alot alike. Best just to call it a white lily, or as I do, a "lost tag" lily. Arc-en-ceil is an easy hardy to identify because of it's pads, and the Indian Goddess lilies are easy to identify because of their blooms, but most others are not so easy. Yours could even be a cross between two different lilies, which means it would be an unnamed lily/