I'll reserve my definition to the end, but I'll post something I just read. I found it interesting, maybe you will too.
WIE:And what kinds of things impede evolution?
MC: Well, I think the great religions were all pretty good at pointing this out, whether we're talking about the five precepts of Buddhism or the capital sins of Christianity. You find that those are pretty much on target, in the sense that they all have to do with things like greed—whether it's gluttony or envy—with wanting things for yourself, trying to get things for free from others by stealing, robbing, cheating, or depriving others of their opportunity to lead a good life. So all these things psychologically go against the development of the soul or the development of complexity because they reduce the person back to his or her biological needs or the conventions of the culture, and they don't allow growth.
By the way, the speaker is no friend of religion. He sees them as largely impeding human growth.
Also, I think for it to be evil there has to be deliberate intent. That is, they WANT to hurt someone else. You know, foolish mistake, weakness, or accident, they account for most bad things that happen. But there are a select few individuals who actually ENJOY inflicting pain on others. They are evil.