Thankless

Part of speech: adjective (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.