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. [1913 Webster]
Hence, a fundamental constitution which guaranties rights and privileges. [1913 Webster]
magna carta, n. (also Magna Charta)
1 a charter of liberty and political rights obtained from King John of England in 1215.
2 any similar document of rights.