a rarely seen, luminous, iridescent cloud shaped like a cirrus or altocumulus, approximately 15 miles (24 km) above the earth, and of unknown composition.
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Also called mother-of-pearl cloud.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
A cloud resembling a cirrus, showing iridescent coloration when the Sun is several degrees below the horizon. These clouds appear mostly during winter in regions of high latitude.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.