The word existed in (at least) two earlier forms—apossoun and opassom—and is from a Virginia Algonquian word the exact form of which is now unknown, but that itself comes from the Algonquian *wa·p-, meaning "white," and *-aʔθemw-, meaning "dog, small animal."
You can, indeed, write opossum and say it like “possum” and be using an officially recognized pronunciation.
Lol. I needed this today.
Please nobody ever do this.
They don't always play dead, our dog cornered one once, and it was hissing at her.