Definition of four hundred in English:
mid 19th century: from Ward McAllister's remark ‘There are only 400 people in New York that one really knows’, later popularized in society reports by the New York Sun. The notion ‘elite’ is said to be from the selection of high-society guests by the socialite Mrs William B. Astor Jr, whose ballroom could hold 400.
Definition of four hundred in:
- US English dictionary