The Collaborative International Dictionary of English v.0.48:

Malignity \Ma*lig"ni*ty\, n. [F. malignit['e], L. malignitas.]
   1. The state or quality of being malignant; disposition to do
      evil; virulent enmity; malignancy; malice; spite.
      [1913 Webster]

   2. Virulence; deadly quality.
      [1913 Webster]

            His physicians discerned an invincible malignity in
            his disease.                          --Hayward.
      [1913 Webster]

   3. Extreme evilness of nature or influence; perniciousness;
      heinousness; as, the malignity of fraud. [R.]
      [1913 Webster]

   Syn: See Malice.
        [1913 Webster]

WordNet (r) 3.0 (2006):

malignity
    n 1: wishing evil to others [syn: malevolence, malignity]
         [ant: benevolence]
    2: quality of being disposed to evil; intense ill will [syn:
       malignity, malignancy, malignance] [ant: benignancy,
       benignity, graciousness]