Ethereal, yet with the familiarity of Lily about it, Lilliandil is a name created by Douglas Gresham for the movie adaptation of The Voyage of the Dawn Treader, based of C.S Lewis's Narnia novels. An unnamed character in the novel, inspired by Luthien and Arwen from Tolkien's Lord of the Rings, Gresham chose the name Lilliandil inspired by the sea of lilies, also known as the Silver Sea, that appears in the book.
 
While Lilliandil as a name doesn't appear in the classic 'canon' of Narnia, it is lent substance by the fact Douglas Gresham is the stepson of C.S. Lewis.

Lilliandil

Lilliandil Origin and Meaning