| A diffuse, veil-like layer of ice crystals at high altitude, sometimes miles thick. Very often gives rise to a 22º halo, and every once in a while a 46º halo; this is one way to tell a cirrostratus from an altostratus, which is veil-like cloud mainly composed of liquid water. A cirrostratus is often associated with the coming of low pressure, so wind and rain frequently occur within a day or so of its being seen.
Occasionally written cirro-stratus. | 
