|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.
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