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thundercloud

[thuhn-der-kloud] /ˈθʌn dərˌklaʊd/
noun
Also, thunderclouds.
Origin
1690-1700
1690-1700; thunder + cloud

cumulonimbus

[kyoo-myuh-loh-nim-buh s] /ˌkyu myə loʊˈnɪm bəs/
noun, plural cumulonimbus.
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.
Also called thundercloud, thunderclouds, thunderhead.
Origin
1885-90; cumulo- + nimbus
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for thunder clouds

cumulonimbus

/ˌkjuːmjʊləʊˈnɪmbəs/
noun (pl) -bi (-baɪ), -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

thundercloud

/ˈθʌndəˌklaʊd/
noun
1.
a towering electrically charged cumulonimbus cloud associated with thunderstorms
2.
anything that is threatening
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
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Word Origin and History for thunder clouds

cumulonimbus

n.

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

Online Etymology Dictionary, © 2010 Douglas Harper
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thunder clouds in Science
cumulonimbus
  (kym'yə-lō-nĭm'bəs)   
Plural cumulonimbi (kym'yə-lō-nĭm'bī)
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.
thundercloud
  (thŭn'dər-kloud')   
See cumulonimbus.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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