The Collaborative International Dictionary of English v.0.48:

Ideal \I*de"al\, n.
   A mental conception regarded as a standard of perfection; a
   model of excellence, beauty, etc.
   [1913 Webster]

         The ideal is to be attained by selecting and assembling
         in one whole the beauties and perfections which are
         usually seen in different individuals, excluding
         everything defective or unseemly, so as to form a type
         or model of the species. Thus, the Apollo Belvedere is
         the ideal of the beauty and proportion of the human
         frame.                                   --Fleming.
   [1913 Webster]

   Beau ideal. See Beau ideal.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Beau ideal \Beau" i*de"al\ (b[=o]" [-i]*d[=e]"al; 277). [F. beau
   beautiful + id['e]al ideal.]
   A conception or image of consummate beauty, moral or
   physical, formed in the mind, free from all the deformities,
   defects, and blemishes seen in actual existence; an ideal or
   faultless standard or model.
   [1913 Webster]

WordNet (r) 3.0 (2006):

beau ideal
    n 1: an ideal instance; a perfect embodiment of a concept [syn:
         paragon, idol, perfection, beau ideal]