nebula

A diffuse cloud of interstellar dust or gas or both, visible as luminous patches or areas of darkness depending on the way the mass absorbs or reflects incident light or emits its own light.

A galaxy. No longer in technical use.

A cloudy spot on the cornea.

A liquid preparation for use in a nebulizer.

A luminous patch in the heavens, far beyond the limits of the solar system.

In pathology, a cloud-like spot on the cornea.

A faint, cloudlike, self-luminous mass of matter situated beyond the solar system among the stars. The term was originally applied to any diffuse luminous region. Now, technically, it is applied to interstellar clouds of dust and gases (diffuse nebula). However distant galaxies and very distant star clusters often appear like them in the telescope, such as the spiral nebula in Andromeda, known now to be a distant galaxy.