Where does “tribuna” come from?

tribuna (Medieval Latin) comes from Latin tribunal, from Latin tribus, from Latin trēs, from Proto-Italic trēs, from Proto-Indo-European *tréyes.

Ancestry of “tribuna”, step by step

Step	Language	Word	Meaning
1	Latin	tribunal	a raised semicircular or square platform, on...
2	Latin	tribus	One of the three original tribes of Rome: Ramnes,...
3	Latin	trēs	three; 3
4	Proto-Italic	trēs	three
5	Proto-Indo-European	*tréyes	—