How’s this:
Evil: “Caused” suffering, basically. Be it physical (pain, hunger) or mental (fear, anguish, sadness, loss). All those feelings are natural; “evil” could be seen as voluntary, thought out actions that inflict these sufferings on others.
An avalanche pinning you under a big rock might cause you pain and anguish, but wouldn’t be evil, since there is no intent or “thought” behind that phenomena.
On the other hand, if someone waits for you to pass by and causes the avalanche to bury you, his action would be considered “evil”.
Good, by opposition, would be actions that reduce suffering in self and others.
There are grey zones too. Stealing from another might be good for the thief, but “evil” from the victim’s point of view.
Stealing bread from a store to feed your kids is another example. Is it wrong? Is it less wrong that letting your kids die?
Personal values will also be considered by individuals when considering right and wrong or good and evil. So getting clear cut definitions for all cases is impossible.
Basically, “good” can be seen as causing the least suffering to the greatest amount of people. “Evil” would be causing the most harm to the greatest amount of people.
People will also value other people diffently. Generally, we value ourselves and our immediate family the most (especially offsprings); then the rest of our family, our neighbors, community, etc. Because of those relative values, people will be willing to cause harm to many “low valued” people if it means less suffering for even one of their “high valued” people; and they will consider that “good”.