from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A cloud resembling a cirrus, showing iridescent coloration when the sun is several degrees below the horizon.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. polar stratospheric cloud
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a luminous iridescent cloud at a high altitude that may be seen when the sun is a few degrees below the horizon
From nacre (from the iridescent coloring of mother-of-pearl).(American Heritage® Dictionary of the English Language, Fourth Edition)