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cumulus

[kyoo-myuh-luh s]
noun, plural cu·mu·lus.
  1. a heap; pile.
  2. a cloud of a class characterized by dense individual elements in the form of puffs, mounds, or towers, with flat bases and tops that often resemble cauliflower: as such clouds develop vertically, they form cumulonimbus.
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Origin of cumulus

1650–60; < New Latin (Latin: mass, pile)
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for cumulus

cumulus

noun plural -li (-ˌlaɪ)
  1. a bulbous or billowing white or dark grey cloud associated with rising air currentsCompare cirrus (def. 1), stratus
  2. histology the mass of cells surrounding a recently ovulated egg cell in a Graafian follicle
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Word Origin for cumulus

C17: from Latin: mass
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 cumulus

n.

1650s, "a heap," from Latin cumulus "a heap, pile, mass, surplus," from PIE *ku-m-olo-, suffixed shortened form of root *keue- "to swell" (cf. Sanskrit svayati "swells up, is strong," Greek kyein "to swell," Lithuanian šaunas "firm, solid, fit, capable"). Meteorological use for "rounded mass of clouds" first attested 1803.

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Online Etymology Dictionary, © 2010 Douglas Harper

cumulus in Science

cumulus

[kyōōmyə-ləs]
Plural cumuli (kyōōmyə-lī′)
  1. A dense, white, fluffy cloud with a flat base, a multiple rounded top, and a well-defined outline. The bases of cumulus clouds form primarily in altitudes below 2,000 m (6,560 ft), but their tops can reach much higher. Cumulus clouds are generally associated with fair weather but can also bring rain when they expand to higher levels. The clouds' edges are well-defined when they are composed of water droplets and fuzzy when made up of ice crystals. 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.