Source : Webster's Revised Unabridged Dictionary (1913)

Irony \I"ron*y\, a. [From {Iron}.]
   1. Made or consisting of iron; partaking of iron; iron; as,
      irony chains; irony particles. [R.]

Irony \I"ron*y\, n.[L. ironia, Gr. ? dissimulation, fr. ? a
   dissembler in speech, fr. ? to speak; perh. akin to E. word:
   cf. F. ironie.]
   1. Dissimulation; ignorance feigned for the purpose of
      confounding or provoking an antagonist.

   2. A sort of humor, ridicule, or light sarcasm, which adopts
      a mode of speech the meaning of which is contrary to the
      literal sense of the words.

Source : WordNet®

irony
     n 1: witty language used to convey insults or scorn; "he used
          sarcasm to upset his opponent"; "irony is wasted on the
          stupid"; "Satire is a sort of glass, wherein beholders
          do generally discover everybody's face but their
          own"--Johathan Swift [syn: {sarcasm}, {satire}, {caustic
          remark}]
     2: incongruity between what might be expected and what actually
        occurs; "the irony of Ireland's copying the nation she
        most hated"
     3: a trope that involves incongruity between what is expected
        and what occurs