(Roman Catholic Church) a diplomatic representative of the Pope having ambassadorial status WordNet 3.0 & Open English WordNet

An apostolic nuncio is an ecclesiastical diplomat, serving as an envoy or a permanent diplomatic representative of the Holy See to a state or to an international organization. Wikipedia

Papal ambassador, diplomatic rank of the Holy See Wikidata

The ecclesiastic title of a permanent diplomatic representative of the Roman Catholic Church to a sovereign state or international organization, who is accorded a rank equivalent to an accredited ambassador, and may also be given additional privileges including recognition as Dean in a country's diplomatic corps. Wiktionary