That's a cool find! Does wood survive 100+ years in the Virginia soil? I suppose there are lots of variables...
Here is a page with some examples but not much specific info. All of them have thread holes, not a slot (presumably for a shank?). Or was yours a two hole that has worn together as one bigger hole?
Davers, I think somebody nailed it in "Today's finds." Thumbwheel for kerosene lamp. That's why it looked familiar to BOTH of us!! And DC Matt - heck YES! I routinely find enfield bullets with the original wood plug still in the back, and occasionally a bullet in wood . . .