The Collaborative International Dictionary of English v.0.48:

Demoiselle \De`moi`selle"\, n. [F. See Damsel.]
   1. A young lady; a damsel; a lady's maid.
      [1913 Webster]

   2. (Zool.) The Numidian crane (Anthropoides virgo); -- so
      called on account of the grace and symmetry of its form
      and movements.
      [1913 Webster]

   3. (Zool.) A beautiful, small dragon fly of the genus
      Agrion.
      [1913 Webster]

WordNet (r) 3.0 (2006):

demoiselle
    n 1: a young unmarried woman [syn: damsel, demoiselle,
         damoiselle, damosel, damozel]
    2: small brilliantly colored tropical marine fishes of coral
       reefs [syn: damselfish, demoiselle]