Tribe, part 1

A quick and hopefully simple question.

I believe I have read that Gallic Teutates, Insular Tuatha (de
Danaan), and Germanic Teutons all stem from a shared root that means
something akin to the word "tribe"; is this correct?

Would anyone be able to give me the archaic forms of this word, such
as the old and proto Germanic forms, as well as early Celtic?

Depending the outcome I'll probably have a follow up question :^)

Thank you!

Sincerely,
Aydan