butterweight

from The Century Dictionary.

• noun More than full weight; a larger or more liberal allowance than is usual or is stipulated for: in allusion to a custom, now obsolete, of allowing and exacting 17 or 18 ounces,or even more, to the pound of butter. In Scotland either tron weight or a still heavier pound was used for butter.

from the GNU version of the Collaborative International Dictionary of English.

• noun Over weight.