Where does “Bisantiwm” come from?

Bisantiwm (Welsh) comes from Latin Bȳzantium, from Ancient Greek Βυζάντιον, from Ancient Greek -ῐον, from Proto-Indo-European -yós — Creates adjectives from noun or verb stems.

Ancestry of “Bisantiwm”, step by step

Step	Language	Word	Meaning
1	Latin	Bȳzantium	—
2	Ancient Greek	Βυζάντιον	—
3	Ancient Greek	-ῐον	diminutive suffix; "suffix forming...
4	Proto-Indo-European	-yós	Creates adjectives from noun or verb stems

Every word from Proto-Indo-European -yós →Every word from Ancient Greek -ῐον →Every word from Ancient Greek Βυζάντιον →