Proper pluralization of commonly used martial arts terms

Every day I see many good martial artists misuse martial arts terms. This is usually not their fault since no one has taught them the correct way to use the terms. A good example is the practice of saying, Senseis, to indicate more than one Sensei. This is incorrect. The word Sensei can be used as it is to indicate one or more people. It does not need to have an "s" added to it to indicate more than one Sensei. The same holds true of many other martial arts terms. Here are a few examples of words that need no "s" to become plural.

Sensei, Katana, Bo, Sai, Shihan, Kata, .....

There are many more,but I think you get the idea.

Best of Luck!