adj.不感謝的；忘恩的；吃力不討好

Giving advice is usually a thankless act. 進(jìn)忠告通常是一種不令人感激的行為。

I did much for him but what I got was only his thankless complaints. 我為他做了那么多，但得到的只是他不知感恩的抱怨。

They seldom labour their wits on thankless task. 他們很少為吃力不討好的工作動腦筋。