I don't even know where I picked it up to know that! 🤔

I just looked up where the term joey comes from, and it seems to be an Aboriginal Australian word for a little animal. Now, Australia has possums, which are very different from opossums (formally the Virginia opossum), and John Smith made records of opossums in the early 1600s, while the term joey wasn't used until the 1800s. I can't find a reference what they called the babies before then.

Before they get fuzz like these guys, I've heard them called pinky opossums.

Also in my searching on the joey term, I saw reference to adults being called "jacks" and "jills," but I can't say I've ever heard active use those terms that I'm aware.