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Meaning of nacreous cloud

na'creous cloud'

Pronunciation: [key]
  1. a rarely seen, luminous, iridescent cloud shaped like a cirrus or altocumulus, approximately 15 mi. (24 km) above the earth, and of unknown composition. Also called
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
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