Where does “gemẽo” come from?

gemẽo (Old Portuguese) comes from Latin Geminus, from Latin geminus, from Proto-Italic jemanos, from Proto-Indo-European yemH- — twin.

Ancestry of “gemẽo”, step by step

Step	Language	Word	Meaning
1	Latin	Geminus	—
2	Latin	geminus	twin; double, paired; a twin
3	Proto-Italic	jemanos	—
4	Proto-Indo-European	yemH-	twin

gemẽo — Etymology, Origin & Word History | Etymology Explorer