Reward, to me implies an after-the-fact transaction with no necessary before-the-fact component to it. I would hope I wouldn't have to explain to you why bribe doesn't work. Any of the words based on incentive could be used in a situation where the incentive is an absence of a negative as easily as a presence of a positive. For example, "Do what I say and I won't remove your kneecaps." That would tend to incent me.