definition of
thankless

[1] #1 thankless a. [ungrateful, unthankful] not feeling or showing gratitude; "ungrateful heirs"; "How sharper than a serpent's tooth it is / To have a thankless child!"- Shakespeare. wn

[2] #2 thankless s. [unappreciated, ungratifying] not likely to be rewarded; "grading papers is a thankless task". wn