gentleman vs Don

gentleman and Don both are nouns.

Word	Noun	Adjective	Verb	Adverb
gentleman	Yes	No	No	No
Don	Yes	No	No	No

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

Other hyponyms of gentleman include gent, gentleman-at-arms.

gentleman (noun)	Don (noun)
a man of refinement	a Spanish courtesy title or form of address for men that is prefixed to the forename
a manservant who acts as a personal attendant to his employer	a European river in southwestern Russia; flows into the Sea of Azov
	Celtic goddess; mother of Gwydion and Arianrhod; corresponds to Irish Danu
	a Spanish gentleman or nobleman