Where does “ἀρκτικός” come from?

ἀρκτικός (Ancient Greek) comes from Ancient Greek Ἄρκτος, from Proto-Indo-European h₂ŕ̥tḱos, from Proto-Indo-European h₂r̥tḱós — destroying.

ἀρκτικός (Ancient Greek): having to do with the Great Bear; northern lands;...

Definitions

ἀρκτικός traces back through two separate lines of ancestry.

Step	Language	Word	Meaning
1	Ancient Greek	Ἄρκτος	Ursa Major
2	Proto-Indo-European	h₂ŕ̥tḱos	bear
3	Proto-Indo-European	h₂r̥tḱós	destroying

Step	Language	Word	Meaning
1	Ancient Greek	ἄρχω	To begin; To lead, rule, govern, command; To be...
2	Proto-Indo-European	h₂ergʰ-	to begin; to command, rule; to begin, rule,...