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> people you'd go out of your way to cause harm to

It should also be pointed out that there are two different directions here. Is an "enemy" someone you would harm, is an enemy someone who would harm you, or must the desire go in both directions? Moreover, in what tense does the problem take place? Perhaps someone harmed you in the past but is no longer trying to harm you. Is that still an enemy? What about someone who is conspiring to harm you, but you don't yet know about the danger. Is that an enemy yet? Another detail to consider is whether a mere competitor, for example an opposing sports team, is an "enemy". The case of intense dislike also possesses some of these specifics.

Edit: Another very important consideration is those who, while not actually trying to harm you, do so indirectly by exploiting you or otherwise trying to control you for their benefit. For example, is a slave owner the enemy of his slaves? If so, then anyone trying to use you without proper concern for your well-being could be considered an enemy.

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I think you don't have consider a person an enemy just because they consider you one. So in the case of someone you don't know is conspiring against you, I would say of course they're not your enemy--that's something you have to decide. An outside observer could say they were your enemy, if they were privvy to more information.

I don't think an otherwise ambivalent slave owner is the enemy of his slaves. Oppressor or something, yes--but not enemy. Some slave holders were certainly the enemies of their slaves, though.