nebula

noun (plural nebulae /-lē/ or nebulas)

• 1 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.
• (in general use) any indistinct bright area in the night sky, for example, a distant galaxy.

• 2 Medicine a clouded spot on the cornea causing defective vision.