If you describe something as unimaginable, you are emphasizing that it is difficult to imagine or understand properly, because it is not part of people's normal experience.
例句
The scale of the fighting is almost unimaginable...戰斗的規模幾乎無法想象。The children here have lived through unimaginable horrors.這里的孩子經歷了難以想象的恐懼。
英漢詞典釋義
adj.
不能想象的；難以想象的；想不到的
Such speed of travel was unimaginable before the railway age.這樣的車速在鐵路時代之前是不可想像的。We all believed it unimaginable that he had lived alone on a deserted island for so long.我們都覺得他在渺無人跡的荒島上住這么久是不可想象的。