Source : Webster's Revised Unabridged Dictionary (1913)

Ungrateful \Un*grate"ful\, a.
   1. Not grateful; not thankful for favors; making no returns,
      or making ill return for kindness, attention, etc.;
      ingrateful. --South.

   2. Unpleasing; unacceptable; disagreeable; as, harsh sounds
      are ungrateful to the ear. -- {Un*grate"ful*ly}, adv. --
      {Un*grate"ful*ness}, n.

Source : WordNet®

ungrateful
     adj 1: not feeling or showing gratitude; "ungrateful heirs"; "How
            sharper than a serpent's tooth it is / To have a
            thankless child!"- Shakespeare [syn: {thankless}, {unthankful}]
            [ant: {grateful}]
     2: disagreeable; "I will not perform the ungrateful task of
        comparing cases of failure"- Abraham Lincoln