E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A trifle; a thing of no consideration. Oh! nothing. A mere bagatelle. In French, Il dépense tout son argent en bagatelles means, he squanders his money on trash. Il ne samuse quà des bagatelles, he finds no pleasure except in frivolities. Bagatelle! as an exclamation, means. Nonsense! as Vous dîtes quil me fera un procès. Bagatelle! (fiddlesticks!)
He considered his wife a bagatelle, to be shut up at pleasure [i.e. a toy to be put away at pleasure].The Depraved Husband.