Origins of the name Hilary
Over time the name developed into Hilary in Britain, and from the Middle Ages onwards was mainly given to boys; this may be largely due to the fame of 4th century religious figure St Hilarius of France.
In the 20th century the name, Hilary was given to both sexes initially (the novelist Evelyn Waugh, bearer of another unisex name, called one of his sons Hilary) but over the century, it came to be seen more as a girl's name.
Is Hilary a girl's name or a boy's name?
Nowadays Hilary is rarely given to boys: The modern US spelling Hillary (also sometimes given in Britain) is used exclusively for girls. This is the spelling of the name Hillary Rodham Clinton, for example, wife of former US President Bill Clinton and current US Secretary of State.