1 [mass noun] a game in which small balls are hit and then allowed to roll down a sloping board on which there are holes, each numbered with the score achieved if a ball goes into it, with pins acting as obstructions.
2a thing regarded as too unimportant or easy to be worth much consideration:dealing with these boats was a mere bagatelle for the world’s oldest yacht club
3a short, light piece of music, especially one for the piano.
mid 17th century(in sense 2): from French, from Italian bagatella, perhaps from baga 'baggage' or from a diminutive of Latin baca 'berry'. sense 1 dates from the early 19th century
bagatelle in other Oxford dictionaries
Definition of bagatelle in the US English dictionary