Pronunciation: (al"tō-strā'tus, -strat'us), [key]
—pl. -tus. Meteorol.
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 ft. (2450–6100 m).
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.