E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Sardonic Smile, Grin, or Laughter.
A smile of contempt: so used by Homer.
The Sardonic or Sardinian laugh. A laugh caused, it was supposed, by a plant growing in Sardinia, of which they who ate died laughing.Trench: Words, lecture iv. p. 176.
The Herba Sardonia (so called from Sardis, in Asia Minor) is so acrid that it produces a convulsive movement of the nerves of the face, resembling a painful grin. Byron says of the Corsair, There was a laughing devil in his sneer.