The island of Sardinia, consisting chiefly of marshes and mountains, has from the earliest period to the present been cursed with a noxious air, an ill-cultivated soil, and a scanty population. The convulsions produced by its poisonous plants gave rise to the expression of sardonic smile, which is as old as Homer (Odyssey, xx. 302).Mahon: History of England, vol. i. p. 287.
The explanation given by Mahon of the meaning of sardonic smile is to be sure the traditional one, and was believed in by the late classical writers. But in the Homeric passage referred to, the word is sardanion ([greek]), not sardonion. There is no evidence that Sardinia was known to the composers of what we can Homer.
It looks as though the word was to be connected with the verb [greek], show the teeth; grin like a dog; hence that the sardonic smile was a grim laugh.M. H. Morgan.