ambassador

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A diplomatic official of the highest rank appointed and accredited as representative in residence by one government or sovereign to another, usually for a specific length of time.
• noun A diplomatic official heading his or her country's permanent mission to certain international organizations, such as the United Nations.
• noun An authorized messenger or representative.
• noun An unofficial representative.

from The Century Dictionary.

• noun A diplomatic agent of the highest rank, employed to represent officially one prince or state at the court or to the government of another.
• noun Hence — In general, any diplomatic agent of high rank; an agent or a representative of another on any mission.
• noun A thing sent as expressive of the sentiments of the sender.

from the GNU version of the Collaborative International Dictionary of English.

• noun A minister of the highest rank sent to a foreign court to represent there his sovereign or country.
• noun An official messenger and representative.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A minister of the highest rank sent to a foreign court to represent there his sovereign or country.
• noun An official messenger and representative.
• noun obsolete, slang A trick to duck some ignorant fellow or landsman, frequently played on board ships in the warm latitudes. It is thus managed: A large tub is filled with water, and two stools placed on each side of it. Over the whole is thrown a tarpaulin, or old sail: this is kept tight by two persons, who are to represent the king and queen of a foreign country, and are seated on the stools. The person intended to be ducked plays the Ambassador, and after repeating a ridiculous speech dictated to him, is led in great form up to the throne, and seated between the king and queen, who rising suddenly as soon as he is seated, he falls backwards into the tub of water. (1811 Dictionary of Vulgar Tongue)
• noun A corporate representative, often the public face of the company.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a diplomat of the highest rank; accredited as representative from one country to another
• noun an informal representative