The Collaborative International Dictionary of English v.0.48:

Missy \Mis"sy\, n.
   An affectionate, or contemptuous, form of miss; a young girl;
   a miss. -- a. Like a miss, or girl.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Missy \Mis"sy\, n. (Min.)
   See Misy.
   [1913 Webster]

WordNet (r) 3.0 (2006):

missy
    n 1: a young woman; "a young lady of 18" [syn: girl, miss,
         missy, young lady, young woman, fille]