The Collaborative International Dictionary of English v.0.48:

Vixen \Vix"en\, n. [AS. fixen a she-fox, for fyxen, fem. of fox.
   See Fox.]
   1. A female fox. [Obs. or Prov. Eng.]
      [1913 Webster]

   2. A cross, ill-tempered person; -- formerly used of either
      sex, now only of a woman. --Barrow.
      [1913 Webster]

            She was a vixen when she went to school. --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

vixen
    n 1: a malicious woman with a fierce temper [syn: vixen,
         harpy, hellcat]
    2: a female fox