Ambassador (noun)

1. A diplomatic official of the highest rank appointed by a country to represent it in another country or at an international organization.
2. A person who acts as a representative or promoter of a particular cause or organization.

Origin:

Late middle english (in the sense "representative or messenger"): from old french, from latin ambactus "servant", from ambactus, ambacti "retainer". the current sense dates from the early 17th century.

Examples:

1. The ambassador presented his credentials to the President.
2. The ambassador was known for his negotiating skills.
3. She became an ambassador for a environmental organization.
4. The ambassador's residence was a large mansion.
5. The ambassador was greeted by a military honor guard.