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cumulonimbus

[kyoo-myuh-loh-nim-buh s]
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noun, plural cu·mu·lo·nim·bus.
  1. a cloud of a class indicative of thunderstorm conditions, characterized by large, dense towers that often reach altitudes of 30,000 feet (9000 meters) or more, cumuliform except for their tops, which appear fibrous because of the presence of ice crystals: occurs as a single cloud or as a group with merged bases and separate tops.
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Origin of cumulonimbus

First recorded in 1885–90; cumulo- + nimbus
Also called thundercloud, thunderclouds, thunderhead.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for cumulonimbus

cumulonimbus

noun plural -bi (-baɪ) or -buses
  1. meteorol a cumulus cloud of great vertical extent, the top often forming an anvil shape and the bottom being dark coloured, indicating rain or hail: associated with thunderstorms
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for cumulonimbus

n.

1887, from cumulo-, comb. form of cumulus, + nimbus.

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Online Etymology Dictionary, © 2010 Douglas Harper
cumulonimbus in Science

cumulonimbus

[kyōōm′yə-lō-nĭm′bəs]
Plural cumulonimbi (kyōōm′yə-lō-nĭm′bī)
  1. An extremely dense, vertically developed cloud with a low, dark base and fluffy masses that tower to great heights. Cumulonimbus clouds usually produce heavy rains, thunderstorms, or hailstorms. Also called thundercloud See illustration at cloud.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.