Greek vs Spartan

Greek and Spartan both are nouns.

Word	Noun	Adjective	Verb	Adverb
Greek	Yes	Yes	No	No
Spartan	Yes	Yes	No	No

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

Greek (noun)	Spartan (noun)
the Hellenic branch of the Indo-European family of languages	a resident of Sparta
a native or inhabitant of Greece

Greek (adjective)	Spartan (adjective)
of or relating to or characteristic of Greece or the Greeks or the Greek language	of or relating to or characteristic of Sparta or its people