The Collaborative International Dictionary of English v.0.48:

Mallet \Mal"let\, n. [F. maillet, dim. of mail. See Mall a
   beetle.]
   A small maul with a short handle, -- used esp. for driving a
   tool, as a chisel or the like; also, a light beetle with a
   long handle, -- used in playing croquet.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mallet
    n 1: a sports implement with a long handle and a head like a
         hammer; used in sports (polo or croquet) to hit a ball
    2: a light drumstick with a rounded head that is used to strike
       such percussion instruments as chimes, kettledrums, marimbas,
       glockenspiels, etc. [syn: mallet, hammer]
    3: a tool resembling a hammer but with a large head (usually
       wooden); used to drive wedges or ram down paving stones or
       for crushing or beating or flattening or smoothing [syn:
       mallet, beetle]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "mallet":
   air hammer, ball peen hammer, beetle, chipping hammer, chisel,
   claw hammer, drop hammer, electric hammer, jackhammer,
   modeling clay, pile hammer, point, raising hammer, riveting hammer,
   rubber mallet, sledge, sledgehammer, solder, soldering iron,
   spatula, steam hammer, stone hammer, tack hammer, triphammer