Armybutton?

[NadiG]

It is 2,5 cm diameters.

 

[nkellam22]

I don't know what makes you think its military, looks civilian to me. A star is a very common design.
It doesn't mean its not a good find though. It looks to be a mid-1700s tombac button.

 

[smokeythecat]

I also agree it's an 18th century civilian pattern.

 

[NadiG]

I think it was the color and the star in the middle, that led me to think about the army, I do not know a lot about buttons, hehe... but your guess sounds fantastic!