papal nuncio vs diplomatist

papal nuncio and diplomatist both are nouns.

Word	Noun	Adjective	Verb	Adverb
papal nuncio	Yes	No	No	No
diplomatist	Yes	No	No	No

As nouns, diplomatist is a hypernym of papal nuncio; that is, diplomatist is a word with a broader meaning than papal nuncio:

papal nuncio: (Roman Catholic Church) a diplomatic representative of the Pope having ambassadorial status
diplomatist: an official engaged in international negotiations

Other hypernyms of papal nuncio include diplomat.

papal nuncio (noun)	diplomatist (noun)
(Roman Catholic Church) a diplomatic representative of the Pope having ambassadorial status	an official engaged in international negotiations