A faint, cloudlike, self- luminous mass of matter situated beyond the solar system among the stars. True nebulæ are gaseous; but very distant star clusters often appear like them in the telescope.
- Astronomy A diffuse mass 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 radiation.
- Astronomy See galaxy.
- Pathology A cloudy spot on the cornea.
- Pathology Cloudiness in the urine.
- A liquid medication applied by spraying.