A diplomat of the highest rank; accredited as representative from one country to another WordNet 3.0 & Open English WordNet

An ambassador is an official envoy, especially a high-ranking diplomat who represents a state and is usually accredited to another sovereign state or to an international organization as the resident representative of their own government or sovereign or appointed for a special and often temporary diplomatic assignment. Wikipedia

Highest ranking diplomat who represents a nation. Wikipedia Disambiguation

Diplomatic envoy Wikidata

A diplomatic official accredited to a foreign sovereign or government, or to an international organization, to serve as the official representative of his or her own country. OmegaWiki

Minister. Wiktionary (translation)

A minister of the highest rank sent to a foreign court to represent there his sovereign or country. (Sometimes called ambassador-in-residence). Wiktionary