cumulus

[kyoo-myuh-luh s] /ˈkyu myə ləs/
noun, plural cumulus.
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.
Origin
1650-60; < New Latin (Latin: mass, pile)
British Dictionary definitions for cumulus

cumulus

/ˈkjuːmjʊləs/
noun (pl) -li (-ˌlaɪ)
1.
a bulbous or billowing white or dark grey cloud associated with rising air currents Compare cirrus (sense 1), stratus
2.
(histology) the mass of cells surrounding a recently ovulated egg cell in a Graafian follicle
Word Origin
C17: from Latin: mass
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.

cumulus in Science
cumulus
  (kym'yə-ləs)   
Plural cumuli (kym'yə-lī')
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.