Thunder clouds

cumulonimbus

[kyoo-myuh-loh-nim-buhs]
noun, plural cumulonimbus.
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

thundercloud

[thuhn-der-kloud]
noun
Also, thunderclouds.


Origin:
1690–1700; thunder + cloud

Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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Collins
World English Dictionary
cumulonimbus (ˌkjuːmjʊləʊˈnɪmbəs)
 
n , pl -bi, -buses
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)
 
n
1.  a towering electrically charged cumulonimbus cloud associated with thunderstorms
2.  anything that is threatening

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Etymonline
Word Origin & History

cumulonimbus
1887, from cumulo-, comb. form of cumulus, + nimbus.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
cumulonimbus   (kym'yə-lō-nĭm'bəs)  Pronunciation Key 
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')  Pronunciation Key 
See cumulonimbus.
The American Heritage® Science Dictionary
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