n. 高层云

[ noun ]
a stratus cloud at an intermediate altitude of 2 or 3 miles
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altostratus \altostratus\, Alto-stratus \Al`to-stra"tus\, n. [L.
altus high + L. & E. stratus.] (Meteor.)
A cloud formation similar to cirro-stratus, but heavier and
at a lower level; a stratus cloud at an intermediate altitude
of 2 or 3 miles.
[Webster 1913 Suppl. + WordNet 1.5]