Where does “Πνύξ” come from?

Πνύξ (Ancient Greek) comes from Ancient Greek πυκνός, from Proto-Indo-European puḱ- — tail; press together.

Ancestry of “Πνύξ”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	πυκνός	thick; dense; sagacious, crafty, cunning
2	Proto-Indo-European	puḱ-	tail; press together

Πνύξ — Etymology, Origin & Word History | Etymology Explorer