What is the opposite of poetess?

There isn't really an opposite of "poetess" in the strict sense. "Poetess" is a term that is often considered outdated and unnecessary, as the term "poet" is gender-neutral.

However, if you're looking for a word that conveys the opposite of a poet, you could consider:

* Prosaist: Someone who writes prose instead of poetry.

* Novelist: Someone who writes novels.

* Essayist: Someone who writes essays.

* Playwright: Someone who writes plays.

* Non-writer: Someone who does not write.

Ultimately, the best "opposite" depends on the context and what you want to emphasize.