n. pl. neb·u·lae (-lē′) or neb·u·las
a. A diffuse cloud 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 light or emits its own light.
b. A galaxy. No longer in technical use.
a. A cloudy spot on the cornea.
b. A liquid preparation for use in a nebulizer.
[Middle English nebule, cloud, mist, from Latin nebula; see nebh- in the Appendix of Indo-European roots.]
(click for a larger image)nebula
the Crab Nebula, photographed by the Hubble Space Telescope in 2005
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.