sardonic versus sarcastic

sar·cas·tic (sär-kas'tik)
adj.

Expressing or marked by sarcasm.
Given to using sarcasm.
[SARC(ASM) + -astic, as in ENTHUSIASTIC.]

sar·cas'ti·cal·ly adv.
SYNONYMS sarcastic, ironic, caustic, satirical, sardonic. These adjectives mean having or marked by a feeling of bitterness and a biting or cutting quality. Sarcastic suggests sharp taunting and ridicule that wounds: “a deserved reputation for sarcastic, acerbic and uninhibited polemics” (Burke Marshall). Ironic implies a subtler form of mockery in which an intended meaning is conveyed obliquely: “a man of eccentric charm, ironic humor, and—above all—profound literary genius” (Jonathan Kirsch). Caustic means corrosive and bitingly trenchant: “The caustic jokes … deal with such diverse matters as political assassination, talk-show hosts, medical ethics” (Frank Rich). Satirical implies exposure, especially of vice or folly, to ridicule: “on the surface a satirical look at commercial radio, but also a study of the misuse of telecommunications” (Richard Harrington). Sardonic is associated with scorn, derision, mockery, and often cynicism: “He was proud, sardonic, harsh to inferiority of every description” (Charlotte Brontë).