Definition of "nebula" []

• 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. (noun)
• Astronomy See galaxy. (noun)
• Pathology A cloudy spot on the cornea. (noun)
• Pathology Cloudiness in the urine. (noun)
• A liquid medication applied by spraying. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "And yet the work of Fabry and Buisson, which has been verified by Professor Frost at the Yerkes Observatory, shows that the nebula is a seething mass of gaseous matter where there is no rest and over whose vast bulk relative motions of several miles a second are constantly, taking place."
• "Fringing the outlines of the nebula is a system of whisker-like rays."
• "The nebula is clearly a planetary nebula, and the gas seen above composed the outer layers of a sun-like star only 10,000 years ago."