altostratus

[al-toh-strey-tuh s, -strat-uh s] /ˌæl toʊˈstreɪ təs, -ˈstræt əs/
noun, plural altostratus. Meteorology
1.
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).
Origin
1890-95; alto- + stratus
British Dictionary definitions for altostratus

altostratus

/ˌæltəʊˈstreɪtəs; -ˈstrɑː-/
noun (pl) -ti (-taɪ)
1.
a layer cloud at an intermediate height of about 2400 to 6000 metres (8000 to 20 000 feet)
altostratus in Science
altostratus
  (āl'tō-strāt'əs)   
Plural altostrati (āl'tō-strāt'ī')
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.