do-

I.

do-, du-

prefix of negative quality, Irish do-, dó-, Old Irish do-, du-, *dus-; Sanskrit dus-; Greek $$Gdus-; Gothic taz-, German zer-. Its opposite is so, q.v. Following the analogy of so, it aspirates the consonants though originally it ended in s.

II.

du-, do-

prefix denoting badness of quality, Irish, Old Irish du-, do-, *dus; Greek $$Gdus-; Gothic tuz-, Norse tor-; Sanskrit dus-. See do-.

III.

to-, do-

verbal prefix = to, ad, Irish, Old Irish to-, do-. Stokes compares Gothic du- to, from þ;u (?). Welsh has du-, dy-, y, Cornish dhi, Breton do, da.