Etymology

meaning 'white (or blank) paper' - the military term for surrender. The term was previously 'charte blanche'. It is first recorded by Raby in 1707 (reprinted in the Hearne Collection, 1886):

"Who sent Chart Blanch to make a Peace."
Soon after that we have a citation that gives a clearer understanding of the meaning - from
Joseph Addison in The Spectator, 1712:

"I threw her a Charte Blanche, as our News Papers call it, desiring her to write upon it her own Terms."

(copied from http://www.phrases.org.uk/meanings/86175.html)

Noun

carte blanche (plural cartes blanches)

1. Unrestricted power to act at one's own discretion; unconditional authority
   • 2001, Oliver Sacks, Uncle Tungsten: Memories of a Chemical Boyhood, Alfred A. Knopf (2001), 15,

     Indeed, I later learned that when they had bought the place, in 1930, they had given my father's older sister Lina their checkbook, carte blanche, saying, "Do what you want, get what you want.