The origins of the name Pit Bull are upsetting and cruel.

The "bull" part of the "pit bull" name comes from the fact that these breeds of dogs were often used for both bear and bull baiting. In some parts of the world, they still are. Baiting refers to the act of tying up an animal, and having it taunted by some exterior force. In this case, the pit bulls would be trained to torment either the bull or bear.
Clearly, this is an extremely cruel and sad answer to the question regarding the origin of the name "pit bull." These animals are taught to despise each other. Furthermore, the situation could quickly become dangerous. The dog has the advantage since the larger animal is tied up; however, if that animal becomes untied, it may quickly go after the dog. This situation is very cruel for both animals, because they are being treated as objects, and not as living creatures.
The term "pit" is much more difficult to define in terms of dogs, and a lack of information exists regarding the nature of this term. However, the most likely reason for this word is that these dogs were "pitted" against other types of animals or other dogs.
Answering the question where did the name pit bull come from reveals some saddening information about the breed. As anyone can see, pit bulls are regarded as vicious dogs because that is how people have trained them to be! Trained properly and with care and affection, as opposed to brute force and maltreatment, pitbulls are loving dogs who make great companions.