Source : Webster's Revised Unabridged Dictionary (1913)

Stunner \Stun"ner\, n.
   1. One who, or that which, stuns.

   2. Something striking or amazing in quality; something of
      extraordinary excellence. [Slang] --Thackeray.

Source : WordNet®

stunner
     n 1: a very attractive or seductive looking woman [syn: {smasher},
           {knockout}, {beauty}, {ravisher}, {sweetheart}, {peach},
           {lulu}, {looker}, {mantrap}, {dish}]
     2: an unexpected and amazing event; "the stunner was what
        happened on Saturday"