The Collaborative International Dictionary of English v.0.48:

Ingratitude \In*grat"i*tude\, n. [F. ingratitude, L.
   ingratitudo. See Ingrate.]
   Lack of gratitude; insensibility to, forgetfulness of, or ill
   return for, kindness or favors received; unthankfulness;
   ungratefulness.
   [1913 Webster]

         Ingratitude, thou marble-hearted fiend.  --Shak.
   [1913 Webster]

         Ingratitude is abhorred both by God and man.
                                                  --L'Estrange.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ingratitude
    n 1: a lack of gratitude [syn: ingratitude, ungratefulness]
         [ant: gratitude]