"figure of speech in which the intended meaning is the opposite of the literal meaning" (usually covert sarcasm under a serious or friendly pretense), c. 1500, from Latin ironia, from Greek eironeia "dissimulation, assumed ignorance," from eiron "dissembler," perhaps related to eirein "to speak," from PIE *wer-yo-, suffixed form of root *were- (3) "to speak" (see verb). Used in Greek of affected ignorance, especially that of Socrates, as a method of exposing an antagonist's ignorance by pretending to modestly seek information or instruction from him. Thus sometimes in English in the sense "simulated ignorance."
For nuances of usage, see humor (n.). In early use often ironia. Figurative use for "condition opposite to what might be expected; contradictory circumstances; apparent mockery of natural or expected consequences" is from 1640s, sometimes distinguished as irony of fate or irony of circumstances. Related: Ironist. A verb ironize "speak ironically" is recorded from c. 1600.