Quite a Question, isn't it? I can imagine asking a Dozen different people, and getting Twelve separate answers.
However, let's try and come up with a Satisfactory Definition that could satisfy Social, Cultural and Ethical Guidelines, while at the same time Satisfying the Rules of Logic and Critical Thinking.
You may have noticed that I Didn't include "Religion'', as a Term that needed to be included in a Universal Definition of Evil.
RELIGION, BY ITS VERY NATURE, IS A SYSTEM THAT REQUIRES FAITH AND ADHERENCE TO SPECIFIC REQUIREMENTS THAT EXIST OUTSIDE THE REALM OF THE NATURAL WORLD.
THEREFORE, ANY SYSTEM OF PROPER MORAL BEHAVIOR THAT IS FOUNDED ON HUMAN REASON AND RATIONAL THOUGHT, CANNOT BE DERIVED FROM RELIGIOUS DOCTRINE. SO ANY DEFINITION OF "EVIL", BEING APPLIED TO HUMAN BEHAVIOR, MUST COME FROM ELSEWHERE.
This is not a Judgment on whether or not Religion is the proper source for finding the Truth about Evil, either the Definition or the Source. However, Since Ethical and Criminal Behavior, in Practical Terms, must be Judged by Legal Systems grounded in the Physical World, THE "SPIRITUAL WORLD" is not a VIABLE ALTERNATIVE.
You have to remember Religious Faith, and any Teachings that stem from such Beliefs, which include Any and All Doctrines about Moral Behavior, are not Revelations to be Denied as Untrue, or even Questioned outside the Realm of a Churches Hierarchy.
The Hierarchy is the Established Authority, within the Particular, Recognizable, and Unique Body of Faith Itself, that Interprets Doctrine from Sources considered to be Divinely Inspired. Decisions are then made, and become Part of Established and Recognized Church Law.
LOOK FOR PART 2.