Source : Webster's Revised Unabridged Dictionary (1913)

Unkind \Un*kind"\, a.
   1. Not kind; contrary to nature, or the law of kind or
      kindred; unnatural. [Obs.] ``Such unkind abominations.''
      --Chaucer.

   2. Wanting in kindness, sympathy, benevolence, gratitude, or
      the like; cruel; harsh; unjust; ungrateful.

            He is unkind that recompenseth not; but he is most
            unkind that forgetteth.               --Sir T.
                                                  Elyot.
      -- {Un*kind"ly}, adv. -- {Un*kind"ness}, n.

Source : WordNet®

unkindness
     n : lack of sympathy [ant: {kindness}]