That which has a dark, lowering, or threatening aspect; that which temporarily overshadows, obscures, or depresses; as, a cloud of sorrow; a cloud of war; a cloud upon the intellect.

To darken or obscure, as if by hiding or enveloping with a cloud; hence, to render gloomy or sullen.

To mark with, or darken in, veins or sports; to variegate with colors; as, to cloud yarn.

To grow cloudy; to become obscure with clouds; -- often used with up.

a group of many insects; "a swarm of insects obscured the light"; "a cloud of butterflies"

make gloomy or depressed; "Their faces were clouded with sadness"