In The Book of Lost Tales it is implied that she was supposed to be the daughter of Manwë and Varda, but Tolkien appears to have changed this in The Silmarillion and most readers accept that she was simply created by Ilúvatar like the Valar.
Her name may come from the Quenya word for "Starlight".
Quenya noun inflection
|Eönwë · Ilmarë · Ossë · Uinen · Salmar · Sauron · Melian · Arien · Tilion · Gothmog|
Curumo (Saruman) · Olórin (Gandalf) · Aiwendil (Radagast) · Alatar · Pallando · Durin's Bane