The whole city was bathed in moonlight, creating a strange sense of unreality.

unreality 是由前缀 un-（表示"非、不"）和名词 reality（现实）组成的复合名词。reality 来自形容词 real（真实的）加上名词后缀 -ity。unreality 字面意思是"非现实状态"，指"不真实感"或"虚幻感"。