The Collaborative International Dictionary of English v.0.48:

Fourpence \Four"pence\, n.
   1. A British silver coin, worth four pence; a groat.
      [1913 Webster]

   2. A name formerly given in New England to the Spanish half
      real, a silver coin worth six and a quarter cents.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fourpence
    n 1: a former English silver coin worth four pennies [syn:
         fourpence, groat]