Definition of: nebula

(neb′yə·lə) noun plural ·lae (-lē) or ·las
1. Astron. A luminous celestial body of cloudlike appearance and vast extent, composed of gaseous or stellar matter in various degrees of density.
2. Pathol. a A speck on the cornea; visual opacity. b Cloudiness of the urine. [<L, vapor, mist]
—neb′u·lar adjective