His Excellency
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
In English law
The title of a viceroy, governor general, ambassador, or commander in chief.
In American law
This title is given to the governor of Massachusetts by the constitution of that state; and it is commonly given, as a title of honor and courtesy, to the governors of the other states and to the president of the United States. It is also customarily used by foreign ministers in addressing the secretary of state in written communications.