What's This Thing? (Victorian Money)

So I recently acquired a B&M coin dealer, and last week I was going through his "random foreign junk, 20c each" bin and found a Victorian coin from 1900! It's partly dateless (the bottoms of all the numbers are worn off) and it definitely spent a long, long time in circulation. My first thought was "ooh, it's a farthing!" based on a purchase I'd just made, but then I got it home. While it looks like a much more worn version of my 1901 farthing (same obverse and reverse), my farthing is about the size of a US nickel and this coin is a tiny bit bigger than a US quarter; also, the reverse is so worn that if there were ever any words on it, they're long gone and of no help to me (for comparison, the surviving legend on the obverse now reads "VI________EI GRA BRITT REGI_______EF. IND. IMP." and even a couple of those letters are worn down).

I don't think pictures would be of much help to me--I've looked up predecimal pictures before and never found anything with something else in the frame for size reference. So what exactly have I got here? I'd like to label it before it goes in with my other Victorian coins.