thank·less /ˈθæŋkləs/
  (a.)不感謝的,忘恩的,不知感恩的
  Thank·less, a.
  1. Not acknowledging favors; not expressing thankfulness; unthankful; ungrateful.
  That she may feel
  How sharper than a serpent's tooth it is
  To have a thankless child!   --Shak.
  2. Not obtaining or deserving thanks; unacceptable; as, a thankless task.
     To shepherd thankless, but by thieves that love the night allowed.   --Chapman.
  -- Thank*less*ly adv. -- Thank*less*ness, n.
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  thankless
       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, unthankful]
              [ant: grateful]
       2: not likely to be rewarded; "grading papers is a thankless
          task" [syn: unappreciated, ungratifying]