German vs Prussian

German and Prussian both are nouns.

Word	Noun	Adjective	Verb	Adverb
German	Yes	Yes	No	No
Prussian	Yes	Yes	No	No

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

Other hyponyms of German include Teuton, East German, Boche, Hun, Jerry, Kraut, Krauthead, Berliner, Bavarian.

German (noun)	Prussian (noun)
the standard German language; developed historically from West Germanic	a German inhabitant of Prussia
a person of German nationality

German (adjective)	Prussian (adjective)
of or pertaining to or characteristic of Germany or its people or language	of or relating to or characteristic of Prussia or its inhabitants