I have this piece in our box of random LEGO. It doesn’t have any studs to connect to so wonder if it’s even a LEGO piece. Added a picture with other pieces for size perspective. (Sorry about that!)
It is not LEGO but a clip for a Playmobil cannon.
This piece doesn't look like any actual Lego piece that I am familiar with. The way the back of it is designed it looks likely that it snaps onto something. I'll throw a guess out here and suggest it possibly came off of a toy train or model train wheel assembly. It looks vaguely similar to the outside section of Lego part# 2878 (Train Wheel RC Train, Holder).