planchet(n = noun.artifact) coin blank - a flat metal disk ready for stamping as a coin;
is a kind of disc, disk
A flat piece of metal; especially, a disk of metal ready to be stamped as a coin. [1913 Webster]
planchet, n. a plain metal disc from which a coin is made.
Etymology:
dimin. of planch slab of metal f. OF planche: see PLANK