greyish or bluish cloud sheet or layer of striated, fibrous or uniform appearance, totally or partly covering the sky, and having parts thin enough to reveal the Sun at least vaguely, as through gro and glass.
High, sheet-like (layered) clouds which are found at an average height of about 3,000 meters (10,000 feet) or 1,700 to 6,000 meters (6,000 to 20,000 feet). They appear fibrous, striated, or lightly striped. The clouds are composed of water droplets and/or ice crystals (unlike the higher cirrostratus which are primarily made up of ice crystals).
A principal cloud type in the form of a gray or bluish (never white) sheet or layer of striated, fibrous, or uniform appearance; very often totally covers the sky and may cover an area of several thousand square miles; vertical extent may be from several hundred to thousands of meters.