The Collaborative International Dictionary of English v.0.48:

Bagatelle \Bag`a*telle"\ (b[a^]g`[.a]*t[e^]l"), n. [F., fr. It.
   bagatella; cf. Prov. It. bagata trifle, OF. bague, Pr. bagua,
   bundle. See Bag, n.]
   1. A trifle; a thing of no importance.
      [1913 Webster]

            Rich trifles, serious bagatelles.     --Prior.
      [1913 Webster]

   2. A game played on an oblong board, having, at one end, cups
      or arches into or through which balls are to be driven by
      a rod held in the hand of the player.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bagatelle
    n 1: a light piece of music for piano
    2: something of little value or significance [syn: bagatelle,
       fluff, frippery, frivolity]
    3: a table game in which short cues are used to knock balls into
       holes that are guarded by wooden pegs; penalties are incurred
       if the pegs are knocked over [syn: bagatelle, bar
       billiards]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "bagatelle":
   a continental, a curse, a damn, a darn, a hoot, bauble, bean,
   bibelot, bit, brass farthing, button, cent, curio, farce, farthing,
   feather, fig, fleabite, folderol, fribble, frippery, gaud, gewgaw,
   gimcrack, hair, halfpenny, hardly anything, hill of beans, jest,
   joke, kickshaw, knickknack, knickknackery, mere nothing, minikin,
   mockery, molehill, next to nothing, peppercorn, picayune, pin,
   pinch of snuff, pinprick, rap, red cent, row of pins, rush, shit,
   snap, sneeshing, sou, straw, toy, trifle, trinket, triviality,
   tuppence, two cents, twopence, whim-wham