It's too thin to be a coin, I think. If you suspect it's silver, do a light scrub with dish detergent and an old toothbrush to get more of the detail out and repost...
Cleaned it a bit more. Looks like a button. Back centers got a small circular indent. I didnt rule out coin at first cause last week I found an 1852 3 cent coin. I was very suprised that its like half the size of a modern dime and half the weight. Felt like it could break very easily.