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]

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