plenipotentiary vs diplomat

plenipotentiary and diplomat both are nouns.

Word	Noun	Adjective	Verb	Adverb
plenipotentiary	Yes	No	No	No
diplomat	Yes	No	No	No

As nouns, diplomat is a hypernym of plenipotentiary; that is, diplomat is a word with a broader meaning than plenipotentiary:

plenipotentiary: a diplomat who is fully authorized to represent his or her government
diplomat: an official engaged in international negotiations

Other hypernyms of plenipotentiary include diplomatist.

plenipotentiary (noun)	diplomat (noun)
a diplomat who is fully authorized to represent his or her government	an official engaged in international negotiations
	a person who deals tactfully with others