Greek

Greek is a person born in Greece, a person who's ancestors were from Greece or the language spoken by people from Greece. (noun)

See Greek in Webster's New World College Dictionary

noun

a person born or living in ancient or modern Greece
the language of the Greeks, constituting a separate branch of the Indo-European language family
ancient Greek, esp. that of the classical period (c. 8th-4th cent. )
☆ Informal a member of a Greek-letter fraternity or sorority

adjective

See Greek in American Heritage Dictionary 4

(grēk)

noun

a. The Indo-European language of the Greeks.
b. Greek language and literature from the middle of the eighth century B.C. to the end of the third century A.D., especially the Attic Greek of the fifth and fourth centuries B.C.
a. A native or inhabitant of Greece.
b. A person of Greek ancestry.
Informal A member of a fraternity or sorority that has its name composed of Greek letters.
Informal Something that is unintelligible: Quantum mechanics is Greek to me.