The origin of William is the Germanic name Wilhelm, meaning "determined defender." It became popular in England when William the Conqueror became the king in the 11th century.
Popular shortened versions in English include Will, Bill, Willie, Billy, and also Liam (which stands at number 75 on the most popular boys names in the US). Female versions in English include Billie and Wilma
The name William stands as the eighth most popular boy's name in the US in 2008, the same position it held in 2007. In fact, the name William has been in the list of top 20 names for over a hundred years.
