Imperiousness is the name of that proud, ordering way of being. If someone speaks imperiously, the quality you are hearing is imperiousness — the feeling that they expect to be obeyed, and that they are a little too sure they deserve it. It is a bookish noun. In everyday talk people more often say she was so bossy, or he talked as if we worked for him. Writers keep imperiousness when they want to name the attitude itself, not just one sharp sentence.