Definition of "sardonic"

[Q]Uivering fears, Heart-tearing cares, / Anxious ſighs, Untimely tears, / Fly, fly to the Courts; / Fly to fond worldings ſports, / Where ſtrain’d Sardonick ſmiles are cloſing ſtill, / And grief is forc’d to laugh againſt her will; / Where mirth’s but mummery, / And ſorrows only real be.

1685, Henry Wotton, “[A Deſcription of the Countrys Recreations.] Poems Found among the Papers of Sir Henry Wotton”, in Reliquiæ Wottonianæ, or, A collection of Lives, Letters, Poems; […] , Fourth edition, London: […] B[enjamin] Tooke, […] and T[homas] Sawbridge […] , pages 390–391

At the opening of thoſe doors, what a ſight it muſt be to behold the plenipotentiaries of royal impotence, in the precedency which they will intrigue to obtain, and which will be granted to them according to the ſeniority of their degradation, ſneaking into the Regicide preſence, and with the reliques of the ſmile which they had dreſſed up, for the levee of their maſters, ſlill flickering on their curled lips, preſenting the faded remains of their courtly graces, to meet the ſcornful, ferocious, ſardonic grin of a bloody ruffian, who, whilſt he is receiving their homage, is meaſuring them with his eye, and fitting to their ſize the ſlider of his Guillotine!

1796, Edmund Burke, “Letter I. On the Overtures of Peace.”, in Two Letters Addressed to a Member of the Present Parliament on the Proposals for Peace with the Regicide Directory of France, London: […] F[rancis] and C[harles] Rivington, […], published 20 October 1796, page 34

The carriage stopped, the doctor alighted, walked swiftly back to where I had also halted, and told me in an excellent sardonic fashion that he feared the road was narrow, and that he hoped his carriage did not impede the passage of my bicycle.

1904 August, A[rthur] Conan Doyle, “The Adventure of the Missing Three-Quarter”, in The Return of Sherlock Holmes, New York, N.Y.: McClure, Phillips & Co., published February 1905, page 309

Another manifestation, significantly reaching its apogee in the midst of Antonine virtues, was the growing popularity of adoxographical exercises. Mock panegyrics were dashed off, not just by sardonic intellectuals such as Lucian, but also by trained courtiers and polished encomiasts of the stamp of [Marcus Cornelius] Fronto.

1979, Carl Deroux, editor, Studies in Latin Literature and Roman History , volume 1, Brussels: Latomus, page 111