plenipotentiary (adj.)

"invested with, having, or bestowing full power," 1640s, from French plénipotentiaire and directly from Medieval Latin plenipotentiarius "having full power," from Late Latin plenipotens, from Latin plenus "complete, full" (from PIE root *pele- (1) "to fill") + potentem "powerful" (see potent). As a noun from 1650s, "person invested with full powers to transact any business," especially with reference to an ambassador to a foreign court or government, given full power to negotiate a treaty or transact other business.