Adjective: thankless thangk-lus
- Not feeling or showing gratitude
"How sharper than a serpent's tooth it is / To have a thankless child!";
- ungrateful, unthankful
- Not likely to be rewarded
"grading papers is a thankless task";
- unappreciated, ungratifying
See also: unappreciative, unrewarding
Antonym: grateful