unprecedented

from WordNet (r) 3.0 (2006)

unprecedented
    adj 1: having no precedent; novel; "an unprecedented expansion
           in population and industry" [ant: {precedented}]

from The Collaborative International Dictionary of English v.0.48

Unprecedented \Un*prec"e*dent*ed\, a.
   Having no precedent or example; not preceded by a like case;
   not having the authority of prior example; novel; new;
   unexampled. -- {Un*prec"e*dent*ed*ly}, adv.
   [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

45 Moby Thesaurus words for "unprecedented":
      beguiling, bewildering, enigmatic, exceptional, extraordinary,
      fabulous, fantastic, fascinating, incomprehensible, inconceivable,
      incredible, indescribable, ineffable, legendary, marvelous,
      miraculous, mythical, noteworthy, outlandish, passing strange,
      phenomenal, portentous, primary, prodigious, prototypal, puzzling,
      rare, remarkable, sensational, strange, striking, stupefying,
      stupendous, uncopied, unduplicated, unexampled, unheard-of,
      unimaginable, unimitated, unique, unparalleled, unreproduced,
      unspeakable, wonderful, wondrous