Don vs gentleman

Don and gentleman both are nouns.

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

As nouns, gentleman is a hypernym of Don; that is, gentleman is a word with a broader meaning than Don:

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