The Collaborative International Dictionary of English v.0.48:

Carte blanche \Carte` blanche"\ [F., fr. OF. carte paper +
   -blanc, blanche, white. See 1st Card.]
   A blank paper, with a person's signature, etc., at the
   bottom, given to another person, with permission to
   superscribe what conditions he pleases. Hence: Unconditional
   terms; unlimited authority.
   [1913 Webster]

WordNet (r) 3.0 (2006):

carte blanche
    n 1: complete freedom or authority to act

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "carte blanche":
   ample scope, authority, blank check, clearance, copyright,
   discretion, dispensation, elbowroom, favor, field, franchise,
   free course, free hand, free play, free scope, freedom,
   full authority, full power, full scope, full swing, grant,
   immunity, indulgence, latitude, leeway, liberty, license,
   long rope, maneuvering space, margin, no holds barred,
   open mandate, open space, patent, permission, play, power,
   power of attorney, prerogative, privilege, range, right, room,
   rope, sanction, say, say-so, scope, sea room, space, special favor,
   swing, tolerance, warrant, way, wide berth



Bouvier's Law Dictionary, Revised 6th Ed (1856):

CARTE BLANCHE. The signature of an individual or more, on a while. paper,
with a sufficient space left above it to write a note or other writing.
     2. In the course of business, it not unfrequently occurs that for the
sake of convenience, signatures in blank are given with authority to fill
them up.. These are binding upon the parties. But the blank must be filled
up by the very person authorized. 6 Mart. L. R. 707. Vide Ch. on Bills, 702
Penna. R. 200. Vide Blank.