What is the opposite of teacher?

There isn't one single perfect opposite of "teacher." It depends on what aspect of "teacher" you want to contrast. Some possibilities include:

* Student: This is the most common and straightforward antonym, representing the reciprocal relationship.

* Learner: Focuses on the act of acquiring knowledge, contrasting with the act of imparting it.

* Pupil: A more formal and often younger version of "student."

The best opposite will depend on the context.