William is a masculine given name of French origin. It became very popular in the English language after the Norman conquest of England in 1066, and remained so throughout the Middle Ages and into the modern era. It is sometimes abbreviated "Wm." Shortened familiar versions in English include Will, Wills, Willy, Willie, Liam, Bill, and Billy. A common Irish form is Liam. Scottish diminutives include Wull, Willie or Wullie (as in Oor Wullie or the play Douglas). Female forms are Willa, Willemina, Wilma and Wilhelmina.
Etymology
William is related to the German given name Wilhelm. Both ultimately descend from Proto-Germanic *Wiljahelmaz, with a direct cognate also in the Old Norse name Vilhjalmr and a West Germanic borrowing into Medieval Latin Willelmus. The Proto-Germanic name is a compound of *wiljô "will, wish, desire" and *helmaz "helm, helmet".
By regular sound change, Proto-Germanic *Wiljahelmaz should have also descended into English as *Wilhelm, but this latter form is unattested...