I'd say certainly a button, just older than we normally dig in the US, so it looks odd to many. (you're in Romania, correct?) When the European folks wake up they could tell you better, but so far I see the similar long shank on 15-17th examples, but no match... But somewhat similar to this; Record ID: DENO-608296 - POST MEDIEVAL button - Database
he says its heavy. that looks almost an inch long. i didnt notice where he was from but a button that big and heavy? new to me. Im also not real familiar with medieval buttons. Just looks like some machine part.