Definition of blue paper in English:

blue paper

noun

  • 1historical
    Blue-coloured paper, typically used for packaging commercial goods, especially sugar; a sheet of this; now chiefly historical.

  • 2rare A light-sensitive paper used for copying maps and plans, typically made by treating the paper with potassium ferricyanide and ferric ammonium citrate; compare cyanotype (now rare).

Origin

Late 16th century; earliest use found in Richard Carew (1555–1620), antiquary and poet.