Sensei meaning

Sensei is a Japanese term of respect. It is used when addressing teachers or professionals such as doctors, lawyers, and others. If Westerners wish to use Japanese words, they should strive to use them in a way that is correct by Japanese standards. 
Sensei always comes after a person's name. Thus Higaonna Sensei not Sensei Higaonna It is used like the similar honorific term -san at the end. Furthermore, because sensei is an honorific term, one must never refer to himself/herself as sensei, as this is seen as arrogant. We call any teacher sensei, whether or not we are actually studying under that person; to fail to do so is deliberately insulting. Respect for seniors continues into daily life in Japan, and, one would hope, this country as well. 
If you hear your sensei refer to an assistant teacher in the Dojo by his/her first name, it does not mean you should as well. That individual is the sensei’s student, but he/she is your senior, and should be addressed as sensei. Remember that karate begins and ends with respect. This is the way you have chosen.
A sensei therefore is someone who has been "born before" you in the system you are studying and is therefore senior to you, or in Shakespearian terms your "better." This is not the same as the western idea of a coach. A sensei can actually do what he teaches; he or she embodies the art, while a coach can teach you how to do something without necessarily being able to perform the skill him or herself.  
Of course you must believe in your sensei, but at the same time you must never surrender the right to think for yourself. Western society stresses the rights of the individual and all karate students and instructors must be aware of that fact. The student should also remember that the teacher has rights and may choose not to live his life according to the student's expectations of how things should be