Hard: Having a relatively high threshold for a variety of stimuli. In other words: less reactive than some other dogs to lower levels of stimuli which may cause another dog (less hard) to react. Some dogs are more sensative and are affected more easily to a particular stimulus which a hard dog may not be as affected by.
Sharp: Something similar to the above, in that a threshold or tolerance is reached earlier than in some dogs.... but sharp more specifically defines what type of reaction a dog has to stimuli. Sharp, meaning assertive, aggressive (not always meaning aggressive in the way of biting or growling)....but aggressive, as in pushy, forward. Doberman fanciers refer to Dobermans, for example as having been more "sharp" in the early days of this breed. Now they tend toward being less "sharp." They were, in their beginnings very much more aggressive than they are now over all.
Dominant: supreme, most important. (I don't think pulling on a leash means a dog is dominant, that he is trying to take over his owner's world, that he is seeing himself as supreme. I don't think dogs think that way, as in having a self image. I think dogs who pull on leashes are eager to go on a walk because there's not much in life which is more fun and they haven't been taught to restrain themselves. Training makes the difference...nothing to do with dominance, IMO) Being eager, pushy, uneducated is not the same thing as staging a coupe or trying to be the most important.
Aggressive: hostile, attacking
Reactive: responding, can mean anything....appropriately or inappropriately...must be taken within the context to know what is meant. ie: dog lunges at the end of the leash toward another dog: I would call that reactive or over reactive. It doesn't specify what is the type of reaction...ie; aggression, excitement, playfulness. There is just a reaction there.