What is the Gaelic word for teacher?

There isn't one single Gaelic word for "teacher." The Gaelic language (depending on which Gaelic you mean - Scottish Gaelic or Irish Gaelic) uses descriptive phrases instead. A suitable translation would depend on the context. For example, you might use words related to:

* Instructor/Tutor: This might involve words related to teaching a skill or subject.

* Educator: This implies a broader role in education.

* Schoolmaster/Schoolmistress: This specifies the location of teaching.

To get a more precise translation, you'd need to provide more context. For instance, "the teacher at the school" would require a different translation than "my piano teacher."