Where does “Pergameus” come from?

Pergameus (Latin) comes from Latin -eus, from Ancient Greek -εῖος, from Proto-Indo-European -iHwós, from Proto-Indo-European -wós — Creates adjectives from verb stems.

Ancestry of “Pergameus”, step by step

Step	Language	Word	Meaning
1	Latin	-eus	argentum + API → argenteus; ferrum + API →...
2	Ancient Greek	-εῖος	Forms adjectives, usually with a meaning of "of"...
3	Proto-Indo-European	-iHwós	—
4	Proto-Indo-European	-wós	Creates adjectives from verb stems

Every word from Proto-Indo-European -wós →Every word from Latin -eus →Every word from Ancient Greek -εῖος →