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]