Yeah, and in math jargon, "onto" is an adjective.
What it meant in German is really of little importance to English-speakers. In English, it came here as a prefix. Every once in a while, though, *fixes become full-fledged syntactic words, as appears to be happening with uber.
Uber is a good lexeme, anyway, though I'm far fonder of it in prefix form than word form.
As for BelleMorte's post - my favorite word in another language has got to be the Latin word "facio" - translates, "I do". The c is hard, by the way.
Then there's "fac", the imperative form, as well as "facit", "he did".