Greek vs Thessalonian

Greek and Thessalonian both are nouns.

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

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

Greek (noun)	Thessalonian (noun)
the Hellenic branch of the Indo-European family of languages	a native or inhabitant of Thessalonica
a native or inhabitant of Greece

Greek (adjective)	Thessalonian (adjective)
of or relating to or characteristic of Greece or the Greeks or the Greek language