Highness vs aristocrat

Highness and aristocrat both are nouns.

Word	Noun	Adjective	Verb	Adverb
Highness	Yes	No	No	No
aristocrat	Yes	No	No	No

As nouns, aristocrat is a hypernym of Highness; that is, aristocrat is a word with a broader meaning than Highness:

Highness: (Your Highness or His Highness or Her Highness) title used to address a royal person
aristocrat: a member of the aristocracy

Other hypernyms of Highness include blue blood, patrician.

Highness (noun)	aristocrat (noun)
(Your Highness or His Highness or Her Highness) title used to address a royal person	a member of the aristocracy