The human will is our rational appetite. It's the thing in us by which we act to get things.
The things we act to get are determined by our intellect. We apprehend things as good, as desirable, under different aspects; sleeping in and getting up, for example, are both desirable, but (for me at least) for quite different reasons. Our intellect chooses between these goods, then hands off the winning good to the will, which then sets about trying to obtain it.
This is all [my crude understanding of] standard scholastic anthropology.
Let me propose this definition of coercion: Coercion is an act whose object is to force the will to desire something the intellect does not propose to the will. (If you prefer your definitions with genera, you can add "belonging to the genus of acts that violate the integrity of the human person.")
What I like about this definition is that it doesn't include acts whose object is to cause the will to desire something the will wouldn't otherwise desire. There has been talk about how imprisonment is coercion, since the prisoner doesn't will to be imprisoned, and how aiming a gun at a criminal and telling him to freeze is a form of coercion.
I see those acts, however, as changing the circumstances according to which the intellect reaches its judgment. The criminal still apprehends not freezing as desirable, but he now also apprehends the good of not being shot.
What concerns me about this proposed definition of coercion is that it might not prove all that useful. The sorts of acts under discussion may not include many that have as their object the substitution of the coercer's will for the coerced's will. And of course, it leaves untouched the question of the morality of changing the circumstances according to which the intellect reaches its judgment.
Still, something like this might unstick one wheel on the, ah, wagon train of public discourse on the moral treatment of prisoners.