noctilucent definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
shining in the night: said esp. of high-altitude clouds (75 to 90 km or 46 to 56 mi above the earth) that reflect twilight to the earth long after sunset or long before sunrise
Origin: nocti- plush lucent
noctilucent definition by American Heritage Dictionary
The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Luminous at night. Used especially of certain high clouds.
noctilucent - Science Definition
Luminous at night. The term is used especially to describe certain high atmospheric cloud formations visible during summer nights at high latitudes.