Magna Carta

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The charter of English political and civil liberties granted by King John at Runnymede in June 1215.
2. n. A document or piece of legislation that serves as a guarantee of basic rights.

Wiktionary

1. n. A charter, granted by King John to the barons at Runnymede in 1215, that is a basis of English constitutional tradition.

GNU Webster's 1913

1. The great Charter, so called, obtained by the English barons from King John, A. D. 1215. This name is also given to the charter granted to the people of England in the ninth year of Henry III., and confirmed by Edward I.
2. Hence, a fundamental constitution which guaranties rights and privileges.

WordNet 3.0

1. n. the royal charter of political rights given to rebellious English barons by King John in 1215