The Collaborative International Dictionary of English v.0.48:

Free silver \Free silver\
   The free coinage of silver; often, specif., the free coinage
   of silver at a fixed ratio with gold, as at the ratio of 16
   to 1, which ratio for some time represented nearly or exactly
   the ratio of the market values of gold and silver
   respectively.
   [Webster 1913 Suppl.]