[ al-toh-strey-tuhs, -strat-uhs ]
/ ˌæl toʊˈstreɪ təs, -ˈstræt əs /
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noun, plural al·to·stra·tus.Meteorology.
a cloud of a class characterized by a generally uniform gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus: of medium altitude, about 8000–20,000 feet (2450–6100 meters).
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Origin of altostratus

First recorded in 1890–95; alto- + stratus
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022

British Dictionary definitions for altostratus

/ (ˌæltəʊˈstreɪtəs, -ˈstrɑː-) /

noun plural -ti (-taɪ)
a layer cloud at an intermediate height of about 2400 to 6000 metres (8000 to 20 000 feet)
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

Scientific definitions for altostratus

[ ăl′tō-strătəs ]

Plural altostrati (ăl′tō-strătī′)
A mid-altitude cloud that extends in flat, smooth sheets or layers of varying thickness. Altostratus clouds generally form between 2,000 and 6,100 m (6,560 and 20,000 ft) and often produce long, steady rain showers. See illustration at cloud.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.