E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Laugh in Ones Sleeve (To).
The French is: Rire sous cape, or Rire sous son bonnet. The German is: Ins faüstchen lachen. The Latin is: In stomacho ridre. These expressions indicate secret derision; laughing at one, not with one. But such phrases as In sinu gaudre mean to feel secret joy, to rejoice in ones heart of hearts.