1. (n.) A faint, cloudlike, mass of interstellar dust or gas\. True nebulae are gaseous; but very distant star clusters often appear like them in the telescope.

2. (n.) A white spot or a slight opacity of the cornea.

3. (n.) A cloudy appearance in the urine.

Black Magellanic Cloud Crab Nebula Gegenschein bright diffuse nebula coalsack counterglow dark cloud dark nebula diffuse nebula dust cloud gaseous nebula nebula of Lyra nebular hypothesis nebulosity nebulous stars planetary nebula ring nebula the Coalsack zodiacal light