diplomat vs ambassador

diplomat and ambassador both are nouns.

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

As nouns, ambassador is a hyponym of diplomat; that is, ambassador is a word with a more specific, narrower meaning than diplomat:

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

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