unthinkable

adj.不可能的；难以置信的；想像不到的

It would be unthinkable to ask him to do that. 叫他做那件事是毫无可能的。

Only the effort of the group can make some unthinkable become thinkable. 大家的努力把一件不可能的事变成可能的。

That this project would achieve ultimate success was unthinkable at the time. 这个项目能获得最后的成功在当时对人们来说是难以置信的。

The stars are an unthinkable distance from the earth. 恒星和地球的距离是难以想像的。