When we predicate "good" and "evil" of things, we generally call them that relatively, according to their natures. A good cat has all the features which indicate perfection in a cat. A bad or evil cat lacks the features which make a cat good. Etc.
There's a funny moment in Jesus's conversation with the Rich Young Man, when the young man calls Jesus "good teacher", and he says "Why do you call me 'good'? No one is good but God alone." Jesus's response is startling and weird to us, because we understand what the young man is saying: he's calling Jesus 'good' according to his role as a teacher, not saying he's good purely and absolutely. But Jesus uses this to suggest something indirectly to the young man: What if the real reason he should call him "good" is because God alone is good purely and absolutely, and Jesus is God? The young man doesn't get it, though.