Is it ensure, insure, or assure?
papal envoy, 1520s, from older Italian nuncio (now nunzio), from Latin nuntius "messenger," from PIE root *neu- "to shout" (cf. Greek neuo "to nod, beckon," Old Irish noid "make known").
a Vatican representative accredited as an ambassador to a civil government that maintains official diplomatic relations with the Holy See. He promotes good relations between the government and the Holy See and observes and reports to the pope on the conditions of the Roman Catholic church in the region. A full nuncio is named only to those countries that adhere to a decision of the Congress of Vienna (1815) that the papal representative automatically becomes dean of the diplomatic corps there. In 1965 the name pronuncio was given to those ambassadors whose rank in the diplomatic corps depends solely on seniority. An internuncio is a Vatican diplomat with the rank of minister plenipotentiary; he is accredited to a civil government and performs duties corresponding to those of a nuncio. Compare apostolic delegate.