The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. Unpleasing; unacceptable; disagreeable; as, harsh sounds
      are ungrateful to the ear.
      [1913 Webster] -- Un*grate"ful*ly, adv. --
      Un*grate"ful*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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: ungrateful,
           thankless, unthankful] [ant: grateful, thankful]
    2: disagreeable; "I will not perform the ungrateful task of
       comparing cases of failure"- Abraham Lincoln