Nebula n. : A faint, cloudlike, self-luminous mass of matter situated beyond the solar system among the stars. True nebulae are gaseous; but very distant star clusters often appear like them in the telescope.

Nebula n. : A white spot or a slight opacity of the cornea.

Nebula n. : A cloudy appearance in the urine.

Example:
what were the conditions prior to the formation of the solar Nebula?

Taxonomy
nebulae, Nebula, emission nebulae, gas, diffuse nebulae, Planetary nebulae, emission, ionized, Supernova remnants, star, free encyclopedia, cloud, reflection nebulae, galaxies, HII regions, PPN, planetary nebula, planets.

Defination from the web:
nebula was a general name for any extended astronomical object, including galaxies beyond the Milky Way (some examples of the older ... One of the best examples of this is the Crab Nebula, in Taurus. The supernova event was recorded in the year 1054 and is designated as SN 1054. ...