without being thanked for something, especially for doing something difficult or unpleasant

Carers work tirelessly, and often thanklessly, looking after friends and family members. 照料者不知疲倦地工作，而且往往是吃力不讨好地照顾朋友和家人。

They're working harder than their spouses, and more thanklessly. 他们比配偶工作更努力，而且更吃力不讨好。

without thanking someone or being grateful for what they have done

This tender devotion was somewhat thanklessly received. 这种温柔的奉献多少有点被不怀感激地接受了。

Humans will take and take thanklessly and thoughtlessly from their environment until all the earth's resources are gone. 人类会毫无感激和考虑地从环境中索取，直到地球上所有资源都消失殆尽。