Charles Hill wrote:
Another thing most people outside of Japan don`t know is that using the terms Osensei and Wakasensei is very common when two generations of "sensei" work in the same place. There is a dental clinic in my town run by a father and son, both named Hayashi. To avoid confusion, one is Osensei and one is Wakasensei. This has to be the origin of our "Osensei" as both Morihei and Kisshomaru were active in the dojo.
This could more likely be the case. When Gichin Funakoshi (father of modern karate and founder of Shotokan/Shotokai) and his son, Giko, were both teaching in the 1930s and mid 40s, the father was referred as O Sensei and the son Waka sensei by their students.