The Collaborative International Dictionary
Thankless \Thank"less\, a.
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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. -
Not obtaining or deserving thanks; unacceptable; as, a thankless task.
To shepherd thankless, but by thieves that love the night allowed.
--Chapman. [1913 Webster] -- Thank"less*ly, adv. -- Thank"less*ness, n.
Wiktionary
n. the property of being thankless
Usage examples of "thanklessness".
Gines de Pasamonte, to whom, along with the other galley slaves, Don Quixote gave his freedom in the Sierra Morena, a charitable act that was repaid with ingratitude and thanklessness by those ill-intentioned and badly behaved people.