Where does “грекъ” come from?

грекъ (Old East Slavic) comes from Church Slavonic грькъ, from Proto-Slavic grьkъ, from Latin Graecus, from Ancient Greek Γραικός, from Ancient Greek γραῖα, from Proto-Indo-European ǵerh₂- — to grow old, to mature.

Ancestry of “грекъ”, step by step

Step	Language	Word	Meaning
1	Church Slavonic	грькъ	—
2	Proto-Slavic	grьkъ	Greek
3	Latin	Graecus	Greek, Grecian, of or pertaining to the Greek...
4	Ancient Greek	Γραικός	Greek; a Graecian, a member of an ancient...
5	Ancient Greek	γραῖα	Graea, Boeotia; Greece
6	Proto-Indo-European	ǵerh₂-	to grow old, to mature

Every word from Proto-Indo-European ǵerh₂- →Every word from Ancient Greek γραῖα →Every word from Ancient Greek Γραικός →