(Astronomy)a cloud of gas and dust in outer space, visible in the night sky either as an indistinct bright patch or as a dark silhouette against other luminous matter (天文)星云 ■(in general use) any indistinct bright area in the night sky, e.g. a distant galaxy (一般用语)雾影;星云状物
(Medicine)a clouded spot on the cornea causing defective vision (医)角膜云翳
语源
mid 17th cent. (as a medical term): from Latin, literally mist'