An antique or vintage aged decorative glass dome. I was unable to research exactly the item, and therefor presume it is a glass dome cover, likely used to cover food items such as pressed butter to keep flies (and in my house's case cats) from landing on it.
Seems to be somewhat "one of a kind" item that would be a nice decorative addition to a county style kitchen, where the use could be varied. The glass is relatively thick. Thank you for looking.