Medieval English form of Hilarius or Hilaria. During the Middle Ages it was primarily a masculine name. It was revived in Britain at the beginning of the 20th century as a predominantly feminine name. In America, this name and the variant Hillary seemed to drop in popularity after Hillary Clinton (1947-) became the first lady in 1993. Famous bearers include American actresses Hilary Swank (1974-) and Hilary Duff (1987-).