Welcome aboard T Net. Might be the top of a powder flask, except there isn't anyplace for a spring or lever to attach. However there were powder flasks that were closed with a stopper, and some had the spring and closing mechanism on the spout, (note the second photo) so it still might be the top of a powder flask.
First thing that came to mind is that its part of a door lock. Sometimes they say YALE above the round hole. LOL! Thats what it looks like to me other then that I have no clue.