Source : Webster's Revised Unabridged Dictionary (1913)

Irreversible \Ir`re*vers"i*ble\, a.
   1. Incapable of being reversed or turned about or back;
      incapable of being made to run backward; as, an
      irreversible engine.

   2. Incapable of being reversed, recalled, repealed, or
      annulled; as, an irreversible sentence or decree.

            This rejection of the Jews, as it is not universal,
            so neither is it final and irreversible. --Jortin.

   Syn: Irrevocable; irrepealable; unchangeable.

Source : WordNet®

irreversible
     adj 1: impossible to reverse or be reversed; "irreversible momentum
            toward revolution" [ant: {reversible}]
     2: impossible to reverse or undo; "an irreversible decree"