There is a slight difference between impede and prevent. To impede would be to stop something that is already in progress, or nearly in progress, it is more like to interfere than to prevent. To prevent means to stop something that has not happened yet. Example: The traffic jam impeded my arrival. I had my dog vaccinated to prevent disease. They are similar, generally you may use prevent to replace impede, but impede does not usually replace prevent.

To impede means either to delay or prevent. Defined in this way, if I prevent something, I always impede it. However, if I impede something, I may prevent it, but it could also mean that I only delay or hinder it.

"impede" means to hinder, obstruct, prevent. I can´t see any difference between these words, but I think "impede" is not a very common word, so I would prefer to use another synonym.

If the verb 'to impede' is the root of the word impedence (impedence describes one of the concepts of electric resistance in alternative current electric circuits) then possibly, to impede means 'to provide resistance' against a certain outcome of an event or to slow down something by resisting against its course or by obstructing its course. e.g. Paul prevented the lady from stumbling by immediately grasping her shoulder (the lady did not fall at all) Paul, by pulling the biker by his outfit impeded his acceleration so the police finally arested him. I hope my example is correct. 'to impede' is a very uncommon verb.

Both prevent and impede refer to different degrees of stoppage of action or progress. To prevent is to stop something effectually by forestalling action and rendering it impossible: bars on one's windows prevents burglars from entering the house. To impede is to make difficult the movement or progress of anything by interfering with its proper functioning: the sheriff knew that keeping the prisoner shoeless would serve to impede his escape over the hot and thorny ground. So, as fdmaxey alluded to above, preventing something actually stops it from happening, but impeding it means that you are just slowing it down from happening.