Answer:
In Japanese it is "Sensei", which also actually is a title given to any teacher, professor, or any other figure of authority in the Japanese language, not just in martial arts. The language can vary in other styles such as Korean, Chinese, etc.
Although you can say "master" a lot of teachers I know who haven't let it go to their head prefer NOT to be called "master". The idea behind that is because you can never truly master the martial arts. It is a life long, continuous study.