The Collaborative International Dictionary of English v.0.48:

groat \groat\ (gr[add]t or gr[=o]t), n. [LG. gr[=o]te, orig.,
   great, that is, a great piece of coin, larger than other
   coins in former use. See Great.]
   1. An old English silver coin, equal to four pence.
      [1913 Webster]

   2. Any small sum of money.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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