adj.不感谢的；忘恩的；吃力不讨好
Giving advice is usually a thankless act. 进忠告通常是一种不令人感激的行为。
I did much for him but what I got was only his thankless complaints. 我为他做了那么多，但得到的只是他不知感恩的抱怨。
They seldom labour their wits on thankless task. 他们很少为吃力不讨好的工作动脑筋。
