Greek vs Grecian

Greek and Grecian both are nouns.

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

As adjectives, Greek and Grecian are synonyms defined as:

Greek and Grecian: of or relating to or characteristic of Greece or the Greeks or the Greek language

Other synonyms of Greek include Hellenic.

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

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