“Sarcasm refers to the use of words that mean the opposite of what you really want to say, especially in order to insult someone, or to show irritation, or just to be funny. For example, saying “they’re really on top of things” to describe a group of people who are very disorganized is using sarcasm. Most often, sarcasm is biting, and intended to cause pain. Irony can also refer to the use of words that mean the opposite of what you really want to say; the “they’re really on top of things” statement about the very disorganized group of people can also be described as an ironic statement. But irony can also refer to a situation that is strange or funny because things happen in a way that seems to be the opposite of what you expected; for example, it is ironic if someone who was raised by professional musicians but who wanted a very different kind of life then fell in love with and married a professional musician.
earlier sarcasmus, borrowed from Middle French or Late Latin; Middle French sarcasme, borrowed from Late Latin sarcasmos “mockery,” borrowed from Late Greek sarkasmós, from Greek sarkázein “to jeer at while biting the lips” (in GALEN; perhaps, if the original sense was “to bite or strip off flesh,” derivative of sark-, sárx “flesh”) + –smos, suffix of verbal action
NOTE: The original sense of the Greek verb sarkázein is conjectural, as all instances referring to jeering or mockery come from late or post-classical sources, generally lexica. The sole significant early uses are in Aristophanes’ play Peace, where the Megarians, while pulling boulders from the entrance to a cave, are described as performing the action of the verb sarkázein “like mean (?) curs,” while perishing from hunger (“hoi Megarês… hélkousin d’ hómōs glischrótata sarkázontes hṓsper kynídia”); and in the Hippocratic treatise “On Joints” (Perì Arthrôn), where the verb is used to describe hoofed animals eating grass. In both cases the interpretation of sarkázein is far from transparent.”