ambassador vs diplomat

ambassador and diplomat both are nouns.

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

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

ambassador: a diplomat of the highest rank; accredited as representative from one country to another
diplomat: an official engaged in international negotiations

Other hypernyms of ambassador include diplomatist.

ambassador (noun)	diplomat (noun)
a diplomat of the highest rank; accredited as representative from one country to another	an official engaged in international negotiations
an informal representative	a person who deals tactfully with others