Sardonic

a. [Fr. sardonique, Sp. & It. sardonico, Lat. sardinius, sardonicus, Gr. σαρδάνιος, σαρδόνιος, either from σαίρω, to grin like a dog, or from σαρδών, a plant of Sardinia, Gr. Σαρδώ, which was said to screw up the face of the eater.] Forced, heartless, or bitter; — said of a laugh or smile; having the appearance of gayety or happiness, but covering pain or misery; concealing bitterness of heart; mocking.

Where strained sardonic smiles are glossing still, And Grief is forced to laugh against her will. Wotton.

Sardonic laugh, a spasmodic affection of the muscles of the face, giving it a horrible appearance of laughter, and said to have been first noticed as the effect of eating the Herba sardonica, a species of Ranunculus, that grows in Sardinia.