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.
Irony must not be confused with sarcasm, which is direct: sarcasm means precisely what it says, but in a sharp, bitter, cutting, caustic, or acerbic manner: it is the instrument of indignation, a weapon of offence, whereas irony is one of the vehicles of wit.
Today, sarcasm is generally understood as saying the opposite of what you mean, with the purpose of insulting someone. For example, a passenger might say "way to go" after the driver turns left...
Idiom sarcasm is the lowest form of wit (Definition of sarcasm from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
SARCASM definition: harsh, cutting, or bitter derision, often using irony to point out the deficiencies or failings of someone or something. See examples of sarcasm used in a sentence.
Definition of sarcasm noun in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more.
Irony employed in the service of mocking or attacking someone is sarcasm. Saying "Oh, you're soooo clever!" with sarcasm means the target is really just a dunderhead.
Have you ever heard someone say something that sounds nice, but you know they really mean the opposite? That’s often sarcasm at work! It’s a powerful tool in communication, and understanding it can make you a better reader, writer, and communicator.