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]

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "groat":
   ace, air pollution, atom, attritus, bawbee, bit, bran, cosmic dust,
   crown, crumb, crumble, dab, dole, dollar, dot, dram, dribble,
   driblet, dust, dust ball, dwarf, efflorescence, fallout, farina,
   farthing, filings, fiver, fleck, florin, flour, flyspeck,
   fourpence, fourpenny, fragment, gobbet, grain, granule, grits,
   groats, guinea, hair, half crown, half dollar, halfpenny, handful,
   iota, jot, kittens, lint, little, little bit, mag, meal, meg,
   minim, minimum, minutiae, mite, modicum, molecule, monkey, mote,
   new pence, np, nutshell, ounce, p, particle, pebble, pence, penny,
   pinch, pittance, point, pony, pound, powder, pussies, quid,
   raspings, sawdust, scruple, shilling, sixpence, smidgen, smitch,
   smut, soot, speck, spoonful, spot, tenner, thimbleful, threepence,
   threepenny bit, thrippence, tiny bit, tittle, trifling amount,
   trivia, tuppence, twopence, whit