It is almost certainly a 17th century copper trading token. Issued in times when currency was not always available to circulate. Tokens were issued by merchants and employers, often to agricultural workers to allow them to buy beer and food in the locality.
I have not seen that specific token before but I have seen Irish trade tokens with stars on them, so that is a possibility.
I have dug over a 100,000 targets in my time with a metal detector. Tokens come up a good amount. I know it looks pretty knackered but yours is in fairly ok condition considering it has spent 3 centuries rotting in soil. I would guess the soil quality is half decent and potentially quite free draining. You will find various George milled coppers and the sort in far worse condition than that.
Lead tokens often pop up as well as lead bag seals. Show up as high conductors and get you excited before they surface and you groan. Marginally better than those annoying cow mastitis tubes. God I find so many of those damned things. Farmers and vets must literally have spent their entire days just littering the countryside.
Best of luck on your future digs.
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