Definition of "unpardonable"

unpardonable

adjective
comparative more unpardonable, superlative most unpardonable
1. impossible to pardon; impossible to excuse or justify
  Quotations
  And you will ſee it really may happen in this very happy land, that men who are rich may commit, with impunity, crimes infinitely more unpardonable, becauſe they are committed with leſs temptation, than thoſe for which “little villains” ſuffer every day—crimes which involve in their conſequences the moſt fatal events.
  1794, Charlotte Smith, chapter XI, in The Banished Man. […], volume II, London: […] T[homas] Cadell, Jun. and W[illiam] Davies, (successors to Mr. [Thomas] Cadell) […], page 236
  "I can understand your being wicked," she said keenly, "but not your being cowardly. That is and was unpardonable."
  1900, Gilbert Parker, An Unpardonable Liar
  To lose a game was bad enough, but to round on a comrade was unpardonable; while to lose from the game a half-back of Cameron's calibre was unthinkable.
  1912, Ralph Connor, Corporal Cameron of the Northwest Mounted Police
  It would be unpardonable to ignore the repeated lessons of history.
  1949, The Department of State Bulletin, volume 20, page 472