Source : Webster's Revised Unabridged Dictionary (1913)

Silver certificate \Sil"ver cer*tif"i*cate\
   A certificate issued by a government that there has been
   deposited with it silver to a specified amount, payable to
   the bearer on demand. In the United States and its
   possessions, it is issued against the deposit of silver coin,
   and is not legal tender, but is receivable for customs,
   taxes, and all public dues.

Source : WordNet®

silver certificate
     n : formerly a bank note issued by the United States Treasury
         and redeemable in silver