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!
Not obtaining or deserving thanks; unacceptable; as, a thankless task.
To shepherd thankless, but by thieves that love the night allowed.
-- Thank"less*ly (#), adv. -- Thank"less*ness, n.
© Webster 1913.