Here's why:
* Diminutives are usually used for people or things that are small or endearing. "Teacher" isn't typically associated with these qualities.
* English doesn't have a strong tradition of forming diminutives with "-y" or "-ie" like some other languages. These suffixes are more commonly used with names (e.g., "Johnny," "Katie") or words like "kitty" or "birdie."
However, you could use these options, although they are informal and might not be appropriate in all contexts:
* "Teach" - This is a shortened form of "teacher" but doesn't carry the same feeling of endearment as a diminutive.
* "Professor" - This term is used for university teachers, but it's not a true diminutive.
* "Tutor" - This refers to a private teacher.
Ultimately, the best way to refer to a teacher in a friendly or informal way depends on the specific context and your relationship with the teacher.