Yaris stems from a goddes in Greek mythology named "Charis" who was the symbol of beauty and elegence. It was combined with the German expression of agreement, "ya". The two combined to "Yaris" and literally mean "an agreement of beuaty and elegence."
....and to "OogaMau", if you are going to list a source, don't lie and say it came from your brain, when you obviously got the answer from the same place I did... the Internet. Specifically, Toyota's web site on the FAQ page.