Where does “do-” come from?

do- (Proto-Celtic) comes from Proto-Brythonic ate-, from Proto-Celtic ati-, from Proto-Indo-European éti, from Proto-Indo-European h₁é, from Proto-Indo-European ǵʰe — Postpositional intensifying particle: indeed, at any rate, in fact.

Ancestry of “do-”, step by step

do- traces back through two separate lines of ancestry.

via Proto-Brythonic ate-

StepLanguageWordMeaning
1Proto-Brythonicate-—
2Proto-Celticati-re-, again, second, further
3Proto-Indo-Europeanétibeyond; over
4Proto-Indo-Europeanh₁éand, then
5Proto-Indo-EuropeanǵʰePostpositional intensifying particle: indeed, at any rate, in fact

via Proto-Indo-European dō

StepLanguageWordMeaning
1Proto-Indo-Europeandō—

Words derived from “do-”

Every word from Proto-Indo-European ǵʰe →Every word from Proto-Indo-European h₁é →Every word from Proto-Indo-European éti →