Source : Webster's Revised Unabridged Dictionary (1913)

Belle \Belle\ (b[e^]l), n. [F. belle, fem. of bel, beau,
   beautiful, fine. See {Beau}.]
   A young lady of superior beauty and attractions; a handsome
   lady, or one who attracts notice in society; a fair lady.

Source : WordNet®

belle
     n : a young woman who is the most charming and beautiful of
         several rivals; "she was the belle of the ball"