Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

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