The Collaborative International Dictionary of English v.0.48:

Nonesuch \None"such`\, n.
   A person or thing of a sort that there is no other such;
   something extraordinary; a thing that has not its equal. It
   is given as a name to various objects, as to a choice variety
   of apple, a species of medic (Medicago lupulina), a variety
   of pottery clay, etc.
   [1913 Webster] Nonet

WordNet (r) 3.0 (2006):

nonesuch
    n 1: model of excellence or perfection of a kind; one having no
         equal [syn: ideal, paragon, nonpareil, saint,
         apotheosis, nonesuch, nonsuch]